We don't recommend 'em for sewage holding
It's almost impossible to secure a bag so that it cannot chafe...they're very prone to blowing out a fitting at the first sign of a clog (not a big deal if it's only holding water, but sewage is another matter!)...and because they're designed to hug the contents, it's just about impossible to prevent odor from forming in a flexible tank and gassing everyone in a 50' radius every time the head is flushed, even if no odor leaks inside the boat. The only material recommended for holding tanks is thick-walled polyethylene. We offer (we're distributors, not mfrs btw...so if bags were a good idea, we'd sell 'em) more than 400 different shapes and sizes, so if you'd like to e-mail me, I'll be glad to help you. peghall@bellsouth.net
