We had a bladder on a previous boat. I was washing it one day and the bilge pump kicked on, which had never happened before. I smelled it before I saw it. The PO had patched a hole on the underside of the bladder, which failed. We replaced the bladder with another bladder and never had an issue, but I have to advise against ever patching a bladder.No one has mentioned bladder tanks yet. My Alerion came with one (I forget the brand) and I have no complaints. Bladders are widely used for fuel and other nasty stuff, so the technology is there. They probably don't make maximal use of the space available, but it is easy to see when you need a pumpout with just a glance. The fittings may not be best positioned for gravity drainage, but customization is possible.