Stainless Steel Black Water Tank -- Good or Bad?

[svamnesty]

The boat was built in 1999 and as near as I can tell the black water tank may be original equipment. I am getting ready to redo/replace all the hoses and have not found any information on whether a 20+ year old tank used to store sewage might still be in good shape. Lots of information to replace aluminum and other types of metal tanks but it appears stainless steel tanks are unusual?

I won't know until I pull the whole thing apart what the inside looks like and when I do that, I will be in a location where it will be hard to order replacement parts. So I am trying to determine if I should purchase a new plastic black water waste tank while I can and assume the stainless one needs replacing?

Any insights?

[peghall]

Replace the tank Urine is so corrosive that it will turn even a 316 stainless steel tank into colander, typically within about 10 years, a bit longer for SS, but nowhere near 20+ years. So it's unlikely that yours is original. If there's an inspection port in the top of it, rinse it out with enough clean fresh water to provide a clean view of the bottom and lower tank walls to check for pitting. How serious the pitting is will tell you how close it is to leaking and will also give you an idea of its age.

If you decide to err on the side of caution and just replace it with plastic, Ronco Plastics is your best source for a tank. They make TOP quality thick-walled (50% thicker than most other mfrs) water and waste tanks for a very reasonable price and have more than 400 shapes and sizes, over 100 of which are non-rectangular, and they install fittings--including diptubes--in the sizes and locations specified by the customer when they make the tank. There are retailers who sell Ronco tanks, but Ronco sells direct for a much lower price...and they're great to work with.

When looking at drawings it's important to know that there is no top or bottom until the fittings go in, and YOU decide where they go. So rotate, flip in any orientation to find the tank that fit your space.
Ronco Plastics marine Tanks Ronco Plastics tank drawings

If the hoses are anywhere near 10 years old, you'd be smart to replace those whether you replace the tank or not, 'cuz they may look fine but rubber and plastics dry over time, becoming hard, brittle and prone to cracking and splitting Raritan SaniFlex is top rated, has a 10 yr(the average working life of any hose) warranty against odor permeation and has the added advantage of being so flexible it can be bent almost as tight as a hairpin without kinking. Don't be spooked by the list price, there are retailers who have it $10-11/ft...still expensive, but worth it if you only to replace 'em every 10 years. Without knowing what part of the US--or even whether you are in the US--I don't know where to send you.

I'm always glad to answer questions, so feel free to ask. I see you've just joined our merry band...welcome to cruisersforum!

--Peggie

[Rapanui]

Our stainless black water tank is 22 years old and so far, no problems. We do not hold the contents for more than a day or 2 and flush the tank with sea water when we empty offshore.

[Mrkva]

We have a boat from 86, so almost 40 years old. The (probably original) hoses were really smelly. Tank is original stainless steel and still works fine, except occasional clogs on the pumpout side. (Not really a tank's fault, there's probably something flushed down that shouldn't have been flushed).

[Muaddib1116]

My 20 year old boat has a stainless holding tank, I believe it's original, no leaks (yet). I have freshwater vacuflush heads though, which might dilute the contents enough to be less corrosive.

[svamnesty]

Thanks for all the replies on your experiences with a stainless steel blackwater tank.

I can't access the inspection port -- the tank is installed up against a ceiling. So I won't be able to determine what the insides look like until I pull the hoses out (which are being replaced - cause they smell to high heaven).

Considering we recently replaced some stainless steel scuppers (original to the boat) that were corroded on the inside. I tend to think the tank may have some corrosion on the inside as well but haven't been able to convince my partner.