SM 422’s black water tanks function normally, for now. During our recent haul out I changed the ball valve in the aft head. During this process I noticed that the tank bottom’s copper fitting was corroded badly across the bottom 2 cm. Above that line, it seemed more solid. I dremeled it level, reattached the hose to the ball valve and all is good, for now.

I can see where this is going and have followed closely the black water tank issues of others intently. I’ve had several clogs in both tanks, have used the rigging wire clear out method, chemicals, etc.

I’m thinking (just thinking for now) about how to fix the problem I see coming. I might cut off the very bottom of the tank which holds the copper fitting and build a resin bottom plate into which an 1-1/2 barb screws, the same barb as the ball valve has. Glass this together and that should prevent corrosion.

My riser is a copper tube with sanitary hose clamped inside the tank. Original. Not sure how that was intended to be maintained, but whatever. For reasons we all understand, waste must enter the tank at the top and thus this riser. But Ive wondered what if the macerator hose ran beside the tank on its way up and entered at the upper side if the tank vs. the bottom riser ? Waste still enters at the top of the tank, but clogs could be resolved really easily, by changing the hose which would be outside the tank. Yes there would be small loss of space, but the time saved in maintenance would be substantial. I’d just cap the existing riser hole and make a barbed side entry port. 

I have the luxury of two working heads, but want to ve ready when the time comes, which I think is near.


Tom and Kirstin
SM2K 422 L’ORIENT
Tahiti

 Tom,

If you search the archives on this, you will find a few options. This is a task just about every Amel owner will need to do unless they buy a boat already where it has been modified satisfactory. Try searching for: Fixing/replacing copper on holding tank

When I did mine, I removed the copper and replaced it with fiberglass pipe I purchased at McMaster-Carr. I used West System's G-Flex resin to make sure the seal was perfect.

The fix is not a daunting as it might seem. I would refrain from cutting or modifying the tank.

Mark- did you replace both fittings (the riser and the exit) or just the exit fitting ? Im worried about the damage that would be done to pvc clearing a clog with spinning rigging wire. Lifting the waste to the top of the tank before it enters is appealing from that perspective. The riser and a $2 joker valve us the only thing preventing an 80 liter tank emptying into your head. I’m quite worried about what condition my riser is in.

Tom and Kirstin
SV L’ORIENT
SM2K 422 
Tahiti

 

 

Tom,

I used fiberglass pipe, not PV. It is much stronger. The thickness of the wall is 1/8".

In all the years we've owned our boat, I never had to clear this pipe with a spinning wire brush. However, we have a Y-Valve fitted in the engine room to select between salt or fresh water flush. 99% of the time, we use fresh water to eliminate any possibly of crystalline buildup. Perhaps this also helps the longevity of the copper riser inside the tank.

When I did the repair, I looked inside the tank and was able to see the inside pipe was in good condition. My thought would be, if this needed replacement, a longer piece of fiberglass pipe could be used and inserted from the bottom.

I am not concerned with 80l of black water finding its way down. My thoughts are, if the upper pipe failed, it would do so slowly like the lower one and there would be indications of a leak before the entire tank emptied. Simply opening the seacock at the first sign of any issue would prevent black water returning. And besides, the area it would leak to is the shower pan, so it's just going to go a different route to the ocean. It's an easy area to hose out if this were to occur.