Perhaps Peggy Hall is best equipped to answer this. I ripped a page out of a recent magazine (I think it was "Boating") which has the following paragraph: "Holding tank math: It's been estimated that the average adult produces 0.7 gallons of waste per day in five flushes. That's 0.14 gallons per flush. I'm thankful that my efficient VacuFlush head only adds 0.2 gallons to this. (Conventional heads can add up to a gallon.) So each flush puts 0.34 gallons into the holding tank. That means my 55-gallon holding tank can handle about 161 flushes. I'm averaging 10 flushes a day, which includes visitors. Ten times 0.34 gallons adds up to 3.4 gallons per day. Which means I can go about 16 days until I am deep in it." I am suspicious that these numbers are two low. What might the numbers be with the average manual toilet? <<<Gary Ritzman>>> M/V Dharma Albin 40 Mercer Island WA