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?
Sounds like it could be something along those lines. We added an Airhead last year too. This season, our solids tank tended to become drier unless we added more moist coco peat. No problems whatsoever with liquids getting into the tank. Our vent line is less than 6 feet up to the cabin top above through a Nicro solar vent. So far, it's worked well. Not a solution, but I think better venting might be a good place to start. 20 feet is a long run.