Shower Sump

[Brian Suhl]

I have an '04 Searay 300 Sundancer with a shower/air cond. condensation sump box under the cabin floor. It is basically a sump pump with float in a plastic box. The overboard drain line evidentally has a check valve in it to keep the water in the line from draining back into the box but this valve is not sealing completely and the line water slowly seeps back into the box so the pump runs for four seconds every 15 minutes. I cannot seem to get to the valve. Is there anything I can dump in to run through the pump that might clean the valve? I am guessing there is soap scum or other keeping the drain back valve from seating properly.