Black water tank (Cannot get answers from dealer or factory)


We have a 2021 303BH Prowler travel trailer. We have been camping in it 3 times so far. I have noticed the black water tank filling up faster than normal usage. When I go to dump the tanks I noticed the grey water tank has barely any water in it. The black tank is always full. I have a portable tank that I have to take with me to dump the tank while at campsite during our trip. Last week I had a suspicion that the sink drained into the black water tank. I ran a water hose in the sink for a little while and turned it off. I checked the grey water tank and it was empty. So I checked the black water tank and it showed 1/3 full. So I opened the toilet valve and looked in there and it was 1/3 full. I called my dealer and they said that Prowler is now plumbing the sink water into the black water tanks to prevent solid buildups in the tank itself. I contacted Prowler on Monday thru email and asked them if this was true and I have not heard back from them yet. It makes logical sense but I have owned several campers and have never seen this type of plumbing before. They also have the grey water and black water tank stickers wrong on the outside of my camper. And yes I know which one is the black water tank and which one is the grey water tank. The shower, bathroom sink, and kitchen sink is supposed to drain in the grey water and the toilet drains into the black water tank. I do know my campers but this has me puzzled and just would like some type of solid confirmation.


Well-known member
A number of people have found this plumbing arrangement over the past year or so. I don't think it's limited to Prowlers. The shower usually fills gray tanks fastest, so if you have only 1 gray tank, perhaps draining a sink into the black tank helps balance how often you need to dump each tank. Regardless of that, most people expect the sinks to drain into gray tank(s).

On our Landmark, we have 2 grays and 1 black. Gray #1 is for the bathroom sink and shower, and must be dumped twice as often as gray #2 or the black tank.


Active Member
I'm not convinced by the explanation (keeping the blank tank from getting "buildups") but it doesn't matter. It might be nothing more than just plumbing the sink to the easiest tank to route to. Maybe there's some obstruction like a heat duct under the floor making it hard to plumb it to the grey.

On my 386BH I got all confused by the valves and had to do some experimentation to figure out what was going on. What I found on my forward tanks was similarly confusing. Usually grey and black have their own valves. On my rear two tanks I have that, and can do the usual dance of dumping the black first, then the grey to help rinse out the pipes.

On my forward tanks I also have two valves... but they're in series not parallel. I have to open the lower valve to dump anything, and that opens the black. I can then open the upper valve and that dumps the grey. The order sounds similar but I cannot dump the grey WITHOUT dumping the black. 90% of the time this is no big deal but if we're dry camping we try to use the rear bathroom exclusively. When I'm using a tote tank e.g. at a state park, I like to just dump the grey since that's the highest usage / need - it keeps the tote tank cleaner.

I think a lot of the time manufacturers are trying their best to come up with innovative floor plans and then just do what they can with the plumbing when they have to figure that out! If you think about all the pipes needing certain angles to drain properly and all the stuff under a typical RV these days it must be quite a challenge...