I have a CD 26. In 2005, my boat storage yard replaced my broken Groco head with a Jabsco Model 29090-2000 manual marine toilet. In 2007, the pump failed and was replaced. No problems in 2008. In 2009, the toilet began back flowing liquid after each use. I do not have a vented loop system. I have an intake hose from the seacock, an out take hose thae runs into a sealed holding tank with top deck pump out, and a screened air hose that vents to the side of the boat. My boat is currently on the cradle and I would like to troubleshoot this as best I can before the Spring launch. I phoned Jabsco who advised me to first disconnect the hoses and double check that there is no blockage before buying any replacement parts. I have never disconnected any hoses and read an article in a recent Sailing magazine that mentioned there is a pressure built up in the hoses. ( My holding tank was emptied before haul out). What steps would you take to trouble shoot this problem?