RV Water & Waste 101 – Black Water, Gray Water & Potable Water Problems To Watch For

dumping-rv-water-tanks.jpg Every self-contained RV has both a clean water system and a waste water system. 

  • The clean water is also called fresh water or potable water.
  • The waste water is also referred to as black water and gray water.

Both, the clean and waste water systems on an RV, can give you problems if you’re not familiar with how to properly maintain them. 

When the dealer demonstrated everything to you about the RV you were buying, he may have missed some helpful information that is necessary to keep your RV’s water systems operating properly.

Here’s what you need to know about black water, gray water, and potable water on your RV…

Understanding RV Water Systems

I’m sure after your introductory tour of your RV, you know where the clean water tank and its filler are located.

You probably also know about the drain valves for the waste tank and how to read the monitor panel for levels of all 3 separate tanks (black, gray, potable). 



Some RV dealers will breeze through pretty fast and overlook a number of ways that you can make life easier for yourself and avoid problems down the road.

These tips might help…


Your RV’s Fresh Water System

You’re probably thinking that you just need to fill the tank with clean water, or hook up the hose. It sounds pretty simple, right? 

Well, there are a few more things to keep in mind regarding your RV’s clean water system…


Potable Water Tips:

rv-fresh-water-holding-tank.jpg#1  Always use a certified potable water hose when filling the tank or hooking to city water.  They are easily identified, as they are white in color.  By being a distinctive color, they will be less likely to be used for other things that may contaminate them.  Potable water hoses are manufactured such that they will not cause a bad taste or odor to the water.  Just remember, they should never be used for anything other than supplying clean water to your RV.

Regular garden hoses are not designed for use with potable water, and they often contribute an unpleasant odor and taste to your water. They may also leach chemicals into your water that could affect your health.  Source

#2  Water hoses must always be protected by a pressure regulator when hooked to the city water port of your RV.  The regulator should be attached to the end of the hose that hooks to city pressure, not the end that attaches to the RV.  You want to protect the hose itself from high pressure, as well as the RV water system.

#3   In the event of contamination, foul odor, or bad taste, you should disinfect your RV water system with household bleach.  Pour 1 cup to 1 gallon of water into an empty tank, then fill the system.  Turn on the pump and run water through all faucets until bleach is smelled.  Let it sit 24 hours, then drain and refill the tank.  Run all faucets until the odor of bleach is gone, this may take a couple tanks of water to get rid of the odor.

#4  When RVing in freezing temperatures, the water hose must be protected from freezing whenever it’s under pressure.  It’s best to use as short a hose as possible, install an electrical heat tape, and wrap the hose with insulation.  One-inch split foam pipe insulation works well to cover the hose. 

Here’s a trick to shorten your hose:  In areas where the ground isn’t frozen, you can dig a shallow hole and bury the bulk of extra length of hose.  Place the coiled bulk of extra hose inside a clean plastic garbage bag and cover it with dirt.  This way, Mother Earth is keeping it warm.

#5  High summer temperatures down south can cause a hose under pressure to weaken and split in the same way that freezing temperatures will cause a hose to fail.  Insulate your water line year round when remaining stationary for long periods of time.

#6  Be sure to drain your water tank after every outing, in order to prevent a foul odor from accumulating due to stagnant water. 

More RV fresh water system tips



Your RV’s Waste Water System

Here again, it appears to be pretty simple. You just hook up the waste hose, stick it into the sewer drain at your campsite, and open the dump valves, right?

You might be thinking that you’re good to go until you’re ready to leave the campsite, but actually you’ve just caused yourself some serious problems.

When you hook your sewer hose to the ground sewer connection, many campgrounds and municipalities require you to use an odor tight connection.  This requires a special hose fitting that didn’t come in the courtesy kit supplied with your RV.  It may be a 90-degree plastic fitting that fits inside your sewer hose, or it might be a rubber donut ring that goes around the outside of the hose. 

Here are some more things you need to know about your RV’s waster water system…

Gray Water Tips:

The gray water is what drains from the kitchen and bathroom sinks and the shower.  Since there is no human waste involved, it is stored in its own tank — the gray water tank.

When you look at your water drain valves the gray water comes down the smaller pipe, as there is no solid matter in the water. 

#1  When you’re boondocking, you may want to dispose of gray water through a garden hose using the water to supply moisture to vegetation or a garden that may be close by.  Do not use your potable water hose to drain your waste tank!  Instead, you will need a special drain cap that downsizes the 3-inch fitting to a garden hose fitting.

#2   When hooked to either a city sewer connection or a garden hose, you can leave the gray water valve open to let it drain as it’s used.

More tips for draining your RV’s gray water tank

Black Water Tips:

rv-black-water-holding-tank.jpgThis is the storage tank for the toilet, and only the toilet.  It’s not an environmentally accepted practice to drain this tank anywhere other than an approved RV dump site. 

Here are some other things you need to know about your RV’s black water tank:

  Do NOT leave the dump valve for the black water open when you are hooked up to a sewer connection at a campsite.  By allowing the water to drain away, the solids will accumulate inside the tank.  In a very short period of time, the tank will fill with a solid mass and the tank will not drain.  You will have a nasty project on your hands if you ever need to clean out a tank in this condition.

#2  Leave the drain valve closed until the tank is getting close to full.  This will give the solids time to break down, and the tank will more easily empty completely when you do open the valve.

Having trouble getting your RV’s black water tank to drain properly?

#3   Always use the approved chemicals in your black water tank.  They not only control odor, but they also help break down the toilet paper and solids.  By using special RV toilet paper (or brands that are designed to break down quickly), you will be less likely to have problems with clogs.

#4  Now, about that wonderful monitor panel that indicates the levels of your tank…  The black water light will probably be accurate during your first outing, as the toilet is used for the first few times.  It’s likely it will never be accurate again.  Bits of toilet paper will hang onto the sensors in the tank giving you readings ranging from partially to completely full, when you know darn well the tank is empty.

TIP: You can waste a lot of time and effort by flushing the tank with clean water, driving around with half a tank of water hoping it will clean off the sensors, and still the lights will show that you have a full tank.  Don’t bother, it’s not that important.  Depending on how many people are using the toilet, just set up a schedule and drain the tank when you think it’s getting close to full.  Once a week, every other day, what ever works for you.

#5   If you remain stationary as a full time RVer (we lived in our 5th wheel trailer for 2 years without moving it), it’s a good idea to clean your black water tank every so often to eliminate any residual buildup of solids.  The easiest way is to stick an old garden hose (green in color, so you don’t mix it up with the RV’s clean water hose) through the toilet and with as much water pressure as is available turn, twist, push and pull it to spray water into as many corners and crevices in the tank as possible.  Many toilets drop straight into the black water tank making this chore easier and more effective.



Many RVs are equipped with enclosed and insulated waste and water tanks, some even have heat from the furnace plumbed directly into the space occupied by the tanks.  These RVs are suitable for year round use.  Those with exposed tanks can’t handle being used in freezing temperatures.  Just one more consideration to keep in mind when your shopping for your next RV. 


Learn more about your RV water system here.

Curtis Carper

I’ve been involved in RVing for over 40 yrs -- including camping, building, repairing, and even selling RVs. I’ve owned, used, and repaired almost every class and style of RV ever made. I do all of my own repair work. My other interests include cooking at home, living with an aging dog, and dealing with diabetic issues. If you can combine a grease monkey with a computer geek, throw in a touch of information nut and organization freak, combined with a little bit of storyteller, you've got a good idea of who I am.

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  • Jeremt

    Thanks Curtis! We are in our travel trailer for the first time and I really needed this information. From one RV’er/diabetic to another, thank you!


    • Curtis

      Jeremy, Glad you found the article helpful.

  • Mitch Beebe

    how to thaw a black water tank

    • Curtis

      Mitch Beebe, I’m assuming you have an exposed black water tank under your trailer.  I’d get a portable salamander style heater and point it under the trailer being careful not to get it so close it damages the trailer.  You might hang a tarp on the opposite side to help keep the heat under the trailer.  Remember you’re dealing with something that can burn your RV to the ground, be careful. The other alternative is wait for a warm day and let Mother Nature thaw it for you, it’s not all that cold yet.

  • Layna

    Can I hook a potable rv holding tank directly to the toilet?

    • Curtis

      Layna, I think you mean “portable” tank, but basically no. I say that because I’m interpreting your thought as using the typical slinky hose from your RV attached to the portable tank and leaving the valves open so waste would run directly to the portable tank. The problem is the liquid would run as expected and the solids would pile up in the black tank of the RV eventually plugging the black tank. This is a real mess to clean out. You want as much water as possible to remain in the black tank to help liquefy the solid waste. Only when the black tank is full should you then open the gate valve and drain it into the portable tank for disposal.

  • http://www.facebook.com/ajusticewhiteman Amber P Justice-Whiteman

    Hey Curtis. I just bought a used RV from a friend. Apparently about 14 months ago they let someone stay in it and unknown to my friend, they were using the toilet. The RV hasn’t been run or moved in the last 14 months and I need to know what I’m up against as far as getting this thing cleaned out ( they also left feces in the toilet bowl itself without flushing it down- not a pretty sight). This is my first RV, so any advice you have on what steps I should be taking to getting this cleaned up would be great, hopefully I can stomach it. Thank You in advance.

    • Curtis Carper

      Amber, This may not be as bad as you think, the key is how long the person used the toilet? If it was for a short period the worse you may need to deal with is the tank needs to be emptied and flushed out with water. If a large quantity of solids has built up in the tank you should add water (at least half a tank) and then drive the RV around so that the sloshing action will help loosen the waste so that it will flush out when you drain the tank. It may take 2-3 flushings of the tank to get it cleaned out but you should be good to go after that.

      • http://www.facebook.com/ajusticewhiteman Amber P Justice-Whiteman

        Alrighty, Im gonna give it a try this coming weekend and see how it goes. I will let you know how it works out. Thank You again for your advice, you are awesome!

  • Jon

    How do you refill black water tank with water after draining it?

    • Curtis

      Jon, Through the toilet. You can hold the valve open on the toilet or use a garden hose. Just be sure to NOT use the white clean water hose.

  • http://www.facebook.com/margaret.t.mccarthy Margaret Tauer Mccarthy

    Hi Curtis, we just bought a new 5th wheel with a smaller black water tank. Just curious how most people take there’s with them. Are they able to store them under the 5th wheel or like on a bike rack? Thanks!

    • Curtis

      Margaret, I’m guessing you’re referring to a portable (blue) waste tank. The back of your pickup truck sounds like the perfect place to me. Some people build platforms off the rear of their RV for extra stuff like BBQ’s or lawn chairs, and yes the blue tote as well.

  • rdblake@insightbb.com

    I have house hold toilet paper in my black tank in my camper, is there anything that will desolve it ?

    • Curtis

      rdblake, All I ever use is regular household toilet paper. It dissolves just fine with water, sewage, or whatever is in your black tank. Just make sure there is plenty of liquid. Being stingy with the water when flushing is what leads to a build up of solid material. When in doubt, add more water.

  • Rob t.

    Is it good to leave the gray tank closed or open? I fear bugs might crawl up the pipes

    • Curtis

      Rob T, It’s a matter of personal preference. It won’t hurt anything and I doubt that bugs would be an issue. Myself I close them when in storage and prefer to leave it closed even when hooked to a sewer connection while camping. My reasoning is the Black tank should be kept closed until it is about full so that the solids flush out when you drain it. If you drain the black tank first, then close the valve that allows all water to go out the flexible sewer hose. Then open the gray water valve. The water will run into the black tank and back flush the black tank to some extent. Then open the main dump valve and allow the gray water to go to the sewer hookup. Your biggest concern should always be making sure the black water tank has the best opportunity to get the solids out.

  • Rob t.

    This is my first RV. I have noticed a stale smell when I use my AC or fan. Am I suppose to clean out the air duct an how would I actually do that? P.S. glad I founx tbis site.

    • Curtis

      Rob t, Spray some air freshener into the intake grill. If you have a ducted air conditioner there may be a foam filter you can remove and wash out. The stale smell should go away with use, if it was in storage or some time.

  • Jim

    have a Forest River R Pod, need to install a longer waste hose holder, where and how do I do it?

    • Curtis

      Jim, Maybe this will work for you. Buy a piece of 6″ PVC pipe long enough to do the job. Cap one end, and install a screw in drain plug fitting on the other. Then attach it under the trailer running across the trailer. You’ll have to decide on your own if this is feasible since I can’t see from here what space you have available.

  • Paul

    Hello Jim,
    I’ve got a tough one…
    I recently bought a 1985 silver streak trailer and upon hooking up to water discovered that the great water tank seems to be nearly full of sediment. It does drain but very slowly and it backs up into the shower easily. Any advice?

    • Curtis

      Paul, That is a strange one. Usually it’s the black water tank that has become plugged up with material. Repeated flushing and driving around with water in the tank is the most often recommended way to liquefy tank residue. My one concern, as it is the gray tank, it is possible someone has let cooking grease wash down the drain. That would make an impossible mass that won’t flush out very easily. Try running a plumber’s snake up into the tank from the drain valve. At least you should be able to ascertain that the problem isn’t just something blocking the drain hole.

      • Paul

        Thanks for your reply, Curtis. I’ll give you some more detail…
        We’ve been renovating the Silver Streak for the last several weeks and plan to use it as a home, not as a travel trailer, per se. As I said, when I first hooked up to our water supply, the drain quickly started backing up, indicating that the tank was full. This obviously came as a surprise. To our knowledge the trailer hasn’t been used in quite some time and we’d only run a few gallons of water through the system. When I first attempted to drain the gray water tank (off into the woods, not a septic tank of any sort) quite a lot of foul smelling, actual “gray” liquid came out. Additionally, there were many chunks of a semi-solid chalky substance. With the drain open I ran both our sinks and the shower for a while with the idea that I would flush the system out. This seemed to be working very well – after a few minutes I had a steady flow of clear water pouring out of the hose. I closed the gray water drain, thinking that we would operate with it closed and empty when the tank became full. I ran some more water and to my surprise, the shower drain backed up quickly once again. However, this time when I opened the gray water drain only a trickle came out. That was a couple of weeks ago. I’ve worked on this periodically since then… I’ve tried snaking from the outside into the tank and down through the shower drain. I’ve plunged the backed up shower drain til I’m blue in the face. Even if I leave the drain valve open, water backs up into the shower after a short time. For example, yesterday I washed a few dishes in the kitchen sink. By the time I was done we had two inches of water in the shower. I’m perplexed, to say the least. At this point, because I’m such a complete loss, I’m considering re-plumbing the drainage system to bypass the gray tank all together. But if there’s some way I can clear the tank, that would certainly be preferable. Ugh. I’ve been reluctant to try Drano or anything like that for fear it might damage the plastic plumbing. Might that help?
        A couple of notes… nothing solid has come out of the drain since that first day. The water that comes out is clearer than at first and not especially foul smelling. Thanks again, Curtis.

        • Curtis

          Paul, One more thought. If it’s possible to run a garden hose down the shower drain, or up through the drain valve the added pressure may blast loose some of the material. I’m as much at a lose as you are as to what’s in the tank. I don’t think Drano would harm anything, RV plumbing is pretty much the same as household plumbing these days. I don’t know how much good it would do either. Good luck!

  • Vicky

    We just bought a 2000 Trail-Lite Trail cruiser and it looked in very clean condition with only three previous owners. We found the black tank not fully cleaned but worked that out. The water tank was half full still. We drained that. We plan to bleach that too. But the gray water tank still registers full. We have tried the Dawn, driving around thing and it went from full to 2/3 but them back up to full. I have OCD and I need my sensors to work properly. Please give me the magic fix that will put my mind at ease besides giving this back to the previous owner?

    • Curtis

      Vicky, OCD… This is going to be a problem for you. If it is a straight shot through the toilet into the black tank you can use a spray wand with a garden hose with good pressure and spray the area where the sensor are for a while. You can also use Rid-X for RV’s : http://tiny.cc/f9tlkx
      in the future to help the waste be digested better. Using RV toilet paper may help too because it breaks down easier. The bad news part is even if you succeed in cleaning the sensors the next time you use the toilet most likely the sensors will get contaminated again. I have seldom paid any attention to my black tank sensors because they just aren’t reliable no matter what you do. I simply keep both gray and black tanks closed even when hookups are available and when the gray tank shows close to full I drain both tanks. Drain the black first using the gray water to clean out your sewer hose when it drains.

      • Vicky

        The black tank is flushed clean and shows empty. The gray tank shows full no matter what we do.
        Sent via the HTC Vivid™, an AT&T 4G LTE smartphone

        —– Reply message —–

        • Curtis

          Vicky, Ah, what I get for reading too fast. So used to complaints about Black tanks my mind assumed that was where the issue was. It’s unusual for the gray tank sensors to be contaminated unless cooking grease got dumped down the sink. The dawn trick should have done the job, the only thought would be to try it again using as hot a water as you can get from the tap. Only fill the tank about half full so there is plenty of sloshing going on and when you drive find lots of corners to make. Beyond that I think you have a wiring issue instead of a contamination issue. You might check to make sure there are no sensor wires disconnected. Beyond that I cant really give you a procedure to check the wiring further.

          • Vicky

            Ok thank you :)

            Sent via the HTC Vivid™, an AT&T 4G LTE smartphone

            —– Reply message —–

  • Jessi

    Thank you! This was so helpful and easy enough to understand.

  • browsha

    Can an RV dealership sell a travel trailer as “new” when there is obvious evidence that the bathroom and potentially the bed has been used? When touring the trailer, we found items of women’s clothing in the cupboard above the bed and stool residue in the commode along with a “sloshing” noise coming from underneath.The salesman stated that it had not been rented out due to lack of license plates. He consulted with the sales manager and they gave assurances that the system would be cleaned out. They also planned on reviewing security tapes to see who the mystery camper was.

    • Curtis

      Broesha, an RV dealer can do whatever they choose to do. It is always buyer beware. if they have the certificate of origin for the trailer it has never been titled in is considered new. Whether or not it was used as a demo model under whatever circumstances is there option. What it all boils down to is if you don’t like the trailer, don’t buy it. You are under no obligation either way.

      • browsha

        Thank you for your time and information. I will keep the “buyer beware” in mind when shopping around.

  • Bernice Gardiner

    Can’t get water or anti-freeze into potable/fresh water tank, could it be venting or maybe plugged up? Any suggestions would be greatly appreciated. Also Just drained all tanks thoroughly and trying to winterize. Thanks

    • Curtis

      Bernice, I’m a little confused. You fill the fresh water tank by the large water fill port on the side of your RV. Hard to believe it is plugged. If you are trying to pump antifreeze through the water system you do no fill the water tank with antifreeze. There should be a shut off between the tank and the pump. Then just drain the water tank and leave it empty. You only pump antifreeze through the RV pump and the water lines. There should be a bypass system so you don’t fill the water heater either. You only want antifeeze in the lines, not in the tanks.

  • Brian

    I have a 1994 Fleetwood Mallard that is only used on weekends at a hunting camp. The toilet is never used. When I remove the black/gray drain cover, water immediately flows out. It has a foul odor and color. I drain the gray tank completely until nothing is running out. Then i pull the black water valve and there is always drainage. I can’t figure why there would be any drainage at all from that tank if the toilet is not used. Is there any connection between the gray and black tanks whereby the black tank could receive overflow from the gray tank?

    • Curtis

      Brian, the answer is in the fact that when you remove the black/gray cover you get some water. The blade valves are leaking some, allowing gray water to back up into the black tank. Not a big deal as long as you continue to drain both as you have been doing.

      • Brian

        So, is it recommended to drain one before the other, or does it matter since there won’t be any solid matter in the black tank?

        • Curtis

          Brian, the general rule is open the black tank first, then open the grey tank after the Black has finished drainingopen the gray valve and drain it. That way the gray water will flush the sewer hose.

  • Brian

    Good information. Thank you!