Still no sewage holding tank on board but fed up with going off to look for a WC when in port? You are bound to have space somewhere near the toilet or deep in a locker for a plastic tank holding between 47 and 112 L. Very easy to put together (see drawing). We offer a complete sewage holding tank kit for self-installation. The kit consists of 7 parts: tank, air vent, swan neck, 12 V sewage pump, carbon filter, Y-valve and tank level gauge with display.