3 Dump Valves


Hello, I gave a 2022 mallard m260 and it had 3 dump valves. In the rear of the unit it had two dump valves marked black and grey. In the front of the unit there is another dump valve that is not Marked. Can anyone please tell me what that dump valve is for? Please advise. Thanks
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Prolifically Gabby Member
Possible that it’s for a second gray tank serving either the kitchen sink or the lavatory/shower. Check your rigs floor plan specs for how many holding tanks it has. Each one should have a separate valve, even if they drain to a common sewer outlet.

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Well-known member
Looking at the floorplan, if I had the right model I was looking at, it seems that would be for the kitchen sink. But to make sure, get some food coloring and mix it in a bucket, then dump it down the kitchen sink. When you dump that tank, you will know for sure.


Well-known member
My advise is to test each tank and plumbing fixture to determine what goes where, plus what valve does what tank, then use a label maker and mark every gate valve. When we took delivery of our 2021 4006 the dealer gave us wrong instructions (4 gate valves for 4 tanks, for 1.5 baths, galley, and w/d).


Well-known member
Another easy way to test it on a full hookup is to make sure you have a clear see-through 45- or 90-degree fitting on at the end of the sewer hose (always good to know when you're done flushing your black tanks, anyway), dump all your tanks, then pick a random drain and dump a gallon or two of water into it. Try the front-most toilet first, work the valve, and if that doesn't put anything out, try your front-most bathroom sink. Etc. Work your way back (don't forget the kitchen sink - the "galley" often has its own tank). You'll figure it out.

For fun, I have a dump valve at the front of my 386BH marked "Grey Tank #1" that's actually connected to my front-bathroom black tank. Maybe you have a similarly mis-labeled valve.


Well-known member
We have 3 tanks and 2 are marked "Grey tank #1 and Grey Tank #2". Have had this coach for 5 years and still not sure which grey is which, but that doesn't bother me cuz they all get drained before we leave. I just kinda mentally figure based on use how much water is going into the grey ones. Bad way I know.