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Stuff coming out of potable water tank

Jun 16, 2020
Hinckley Sou’wester 30 Falmouth ME
The previous owner of my boat noted that he had begun to get dark flakes/debris coming through the potable water system and suggested I have the boatyard steam clean it. The yard said they didn’t steam clean tanks because of the baffles and put bleach in instead. I didn’t ask how much (not realizing until reading this forum that there was a debate), but after flushing the tank 2-3 times this summer, I still have stuff coming out that looks like the picture. It is a monel tank. Any suggestions?



Jan 6, 2006
Beneteau 423 Mt. Sinai, NY
Do you have a access port to see inside the tank? Looks nasty! My old boat had a black tank when I bought her..... I first scrubbed her out..... long handled brush with bleach and soapy water. I also used a shop vac to empty the tank and crap. Once I got the stuff out I filled with water and bleach solution and turned on all spigots until I smelled bleach. Then I let sit for a while. But also remember your hoses are probably just as nasty and may be in need of replacing.
My tank on old boat (and new boat) had no baffles....

good luck
Nov 26, 2012
Hunter 34 Berkeley
Do the bleach procedure outlined in Peggy Hall‘s book. Rinse and repeat until nothing comes out. Per the book it’s the lines more than the tank that need it.
Dec 31, 2016
Beneteau Oceanis 351 Charlottetown
Often forgotten is the inside top of the tank, as almost always when you look through the access all you can see are the sides and bottom. When the tank is filled and your boat gets even a slight heel or bouncing around in rough weather, the water will sometimes self clean the top and deposits formed there will dislodge .
Jul 5, 2011
Oday 28 Madison, CT
You may have that slimy, gooey pasta like stuff I had. It will not pump out without blocking the strainer (hope you have or you may block the pump!) I did what others have done and cut a hole in the top and installed an access port, screw thread. Just to a search for "how to" on that. This resulted in my being able to wipe out most of the tank with a micro fiber towel and control this kind of crap. Bleach kills germs, yes, but won't dissolve all types of junk in your tank.
Jul 5, 2011
Oday 28 Madison, CT
Yep. Use a good micro fiber cloth. One guy said he uses a shop vac. Have not tried, but might be an idea as wet or dry.