Check out Pooh Powder, the most absorbent material I have ever seen. Sprinkle a bit on the top of a glass of water and the whole glass full turns to gell. A ten pound bag from the source should last years ,if you only use a sprinkle or two , only when needed.I put an airhead in my boat last spring. Have had alot of problem with excessive moisture in the poop tank. I recently re-mounted the unit so it slopes forward, so the urine will flow better to the urine tank. When I vented the unit, I was uncertain if it would work properly and did not want to hole my deck above the head, so ran a vent line aft to a dorade in the lazarette, about 20 feet, up sloping. I'm wondering if water is condensing (sp) in that line and dripping back into the poop tank. I'm finding that with two people after about a week the unit needs emptying, disappointed so far with the system. Any ideas anyone?