The “Air Head” Composting Toilet works simply. By separating liquids from solids, the volume of solid human matter is significantly reduced. Air Head’s approximate five-gallon capacity means that up to a season’s worth of weekend use may be held. (Based on solid matter volume for two persons’ use twice every weekend for five months: 80 uses). A liveaboard couple can expect 60 uses (one month) before they’ll have to empty the solids tank.