Friday, October 22, 2021


Really? Does your RV’s bathroom sink drain into the sewer tank?

Most RVers assume the sinks in their RV drain exclusively into a gray holding tank. The toilet, most RVers believe, drains exclusively into the black (sewer) tank. But is that always true? In this eight-minute interview by editor Chuck Woodbury with RV waste systems authority Doug Swarts of, you’ll learn that sometimes the bathroom sink does, in fact, drain into the black tank.

Doug even points out that at least one manufacturer drains the liquids from the sink, shower and toilet into the same tank!

While it may be no big deal to most RVers where the water in their bathroom sink drains, to some it can, indeed, be a big deal when conservation of liquid waste is important — as in boondocking, when every ounce of waste liquid matters.

After you watch the video, please answer our brief poll directly below the video. Do you know where the water in your bathroom sink drains?

Okay, would you now please take our survey. Thanks.




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Randy R
2 months ago

The first simple check I will perform when I get my RV in Oct is to open the black and grey water tank and take a hose inside the unit and run water into each sink, toilet, and shower drain until the water runs out! That way I can confirm which drain runs to which holding tank! For used units, You can do the same after dumping and flushing both holding tanks.
Happy Camping!

Bob p
2 months ago

My first tt drained the bathroom sink into the black tank. I was told that was to insure there was plenty of water for the black tank to function properly. It was a 24 1/2’ 1978 CampMate by Tech.

Ed Silva
2 months ago

In the late 80’s, when I ordered a new fifth wheel, manufactured in Washington, the dealer told me that the bathroom sink drained into the black tank to make sure it would have enough liquids, also that there were a couple states that it was a law that the black tank needed an additional drain source other then just one.

Kevin B Loughin
2 months ago

Yep, my Thor Chateu bathroom sink drains into the black tank.
Just this morning, I had to pull the check valve on the sink drain pipe since it seemed to be stuck open and the RV smelled like a sewer.
I found the valve full of maggots! Ugh!
Dam* flies.

Bob S
2 months ago

Our main bathroom sink goes to a gray tank. The sink in our second bathroom drains into the 2nd black tank

Ronald Russell
2 months ago

I sold my 2011 Damon Daybreak 27PD, last December. I discovered, early that my shower emptied into the black tank. Whenever the black got near dump time, I would run the shower till it got 2 or 3 inches of water. Then would drain black tank, and rinse shower.

2 months ago

We have a 2003 Dutchman Express 26Q. I found out pretty quickly that the bathroom sink drains to the black tank. Since the grey water tank is only 20 gallons (probably the smallest in the industry) and the black is 25 I guess it’s not such a bad thing.

2 months ago

I have a 2014 Winnebago Adventurer. I know that my sinks drain into the gray tank and the dealer told me the washing machine also drained to the gray tank. Imagine my surprise when the black tank filed up when doing our first load of clothes.

3 months ago

We just bought a ’71 Ozark Luxury Liner – it has no bathroom sink. The kitchen sink and toilet drain into an exterior portable black tank. The shower drains onto the ground. It looks like originally there was a single black tank on the underside for all three (I can see where the straps were). We may keep the exterior black tank, but we’ll be redoing the entire drain system.

Name courteously withheld.
4 months ago

Draining to the black tank can result in the SPRAYING OF SEWAGE when you open the toilet drain valve…

When the black tank gets over-full (because say you’ve only used the bathroom sink and not the toilet), and then the sink drain backs up, then the PRESSURE upward on the toilet drain valve is POSITIVE (about 3 ft of head). This will result in a surprise sewage spray when you open the toilet drain valve, or at least the possibility of sewage leaking around the toilet valve and into the bowl.

I just discovered this draining into the black tank on my ’94 Fleetwood Southwind when, while doing maintenance on the toilet and washing my hands in the sink, I HEARD it draining into the black tank. Otherwise, I would have had no clue.

10 months ago

Easy to find out. With all tanks empty. Open the black water drain. Turn on faucets and shower see if any water comes out black water drain.

Tom Macfarlane
11 months ago

I assume it goes into the gray tank, and I know for sure that the shower water does.

Robert Lea
11 months ago

I was mystified by how fast my black tank filled up while parked for the winter at a FL RV park. I was dumping it about every 4 days. No way were we using the toilet that much. A neighbor suggested that perhaps another fixture, such as the bathroom sink, was draining into the tank. So I performed a simple test.

Robert Lea
11 months ago
Reply to  Robert Lea

Simple test (continued): drain both black & grey tanks & flush. Run substantial quantity of water down the drain of suspect fixture. Open black tank dump valve. Any water discharged? Open grey water dump valve. Any water discharged? You will easily determine where each fixture drains to. What did I find? The kitchen sink drained into the black tank! That’s why we were filling the black tank so quickly! Now I’m trying to determine if and how I might replumb the drain. Doesn’t look good.

11 months ago

I have a 1955 Spartan Mansion (32 ft) trailer that was originally a park model with no tanks. The toilet sits between the two axles with minimal clearance so the best design I could come up with is a 26 gallon black tank for my toilet, kitchen and bathroom sink connected to a 12v macerator pump (which pumps to another 26gallon auxiliary tank, then to my sewer connection. My shower is on a separate 26 gallon gray tank with a separate sewer connection so in total I have 72 gallons of gray/black storage. I bought the tanks from Elkhart Plastics which was the only tank supplier that had a tank with the dimensions i needed.

It works great but I dread the day the macerator pump breaks. Macerator pumps are used in boats all the time so they do have a good track record.

11 months ago

The manual says the bathroom sink drains into the black tank. I know this is right because you can smell the fumes coming out of the sink when water is running or when we are driving. Thought I’d put in one of those white things you see advertised that take out the u-joint and says it stops the stink. Turns out there is already one there. I now leave the plug in all the time with a cup of water in the sink. No more stink. Have to be careful brushing teeth not to get a mouthful of stinky air when spitting.

Norm Worthington
11 months ago

We have a 2017 Redwood and while just getting it back from the factory shop (4th time) we wanted to be sure that they fixed ALL the tank level indicators. With empty tanks we first stuck a garden hose into the kitchen sink and filled it until it was backing up in the sink…ok. that one’s full….however the indicator showed 1/3 filled. Then to the shower…same thing, filled till I had water above the drain (indicatorshows 2/3d full)…well, might as well flush the bathroom sink a little to clean the gooseneck… my surprise the water level in the shower didn’t come up…? but we checked the black tank and showed enough water in it to light up the black tank indicator. Finished by filling the black tank with the hose. my thought is that the drain for the washer (prep) was going into the shower gray tank instead of the black. The tanks all needed fresh cleaning anyway…found out I can take longer showers now!☆

Cheryl Sheldon
11 months ago

I have a Heartland Edge M18. I haven’t confirmed but suspect the sink drains into the black tank based on how quickly the black fills.

John Koenig
11 months ago

Something related but not mentioned: I’ve seen standard RV “drop” toilets (as opposed to macerating toilets) where there is a SHARP BEND (think ~ 90º) IMMEDIATELY and, the “solid waste” MUST make said sharp bend before it is carried off to the black tank. In stick & brick homes, waste lines MUST be CAREFULLY installed. I believe the the requirement is 1/8″ drop for each 12″ of pipe run. That’s a VERY small margin. More than 1/8″ drop allows liquid to drain faster than it can carry solid waste away. Less then 1/8″ drop allows the solids to collect IN the pipe rather than be carried away. This means that LEVELING the RV would be critical (even more so than an RV refrigerator requires). Fail to achieve this high level of accuracy when leveling an RV virtually guarantees plumbing problems. I saw this type of drop toilet at an RV rally. I have no idea if this installation technique is commonplace. RVers with this plumbing should probably use extra water when flushing solid waste.

Mary Hazel
11 months ago

My 84 Toyota Dolphin front bath has sink and shower draining into black tank-found out hard way. Ugh. After much research on replumbing etc I switched to a C-Head compost toilet and now have 2 grey tanks and no black tank. All working very well!

Ron Hale
11 months ago

We discovered the bathroom sink drains to the black tank shortly after we purchased our Class C motorhome. I found a deep plastic kitchen food storage container that fits perfectly in the sink, which we use for tooth brushing, shaving, etc. Then it is dumped down one side of the kitchen sink, and into the grey tank. Helps keep the black tank from filling so quickly.