Late last season I had the pleasure of a sailing guest aboard the boat leave the head pump valve lever in the wet flush position and not in the dry bowl closed position - after having received careful instruction on using the head before leaving for Block Island. The end result was 18 gallons of sea water in the holding tank and the head overflowing into the bilge with no way to pump out the holding tank as the boat was only set up for deck pump out. Nothing like bringing 18 gallons of Block...