Know it's been posted before but can't seem to find anything. trying to find the best way to calculate holding tank and freshwater tank sizes. Also, opinions on the 'kiss' holding tank idea, my boat currently has just an open space, two seacocks, and clips for a porta potti (not an option) in the head looking for an easy, cheap, and extremely reiable system, but don't want to go crazy on construction, and most importantly want it to last. Actualy I want it to be as close to forgetable as possible. Should mention I will likely be building the tanks because of the odd shapes where I want to mount them, possibly fiberglass more likely metal, any recomendations on the prefered material and gauge? layout of openings etc? would a top mounted discharge with a pickup tube and sump be better than a direct bottom discharge? I have to spend some time going through the archives, seem to remember reading the answers to at least part of these questions before! Was finishing up some projects and will be ready in a week or to to start in the head and realized I didn't have any ideas other than I needed one! Thanksken