Attwood 500 GPH Shower Sump MK2 System - 12V [5141-4]500 GPH Shower Sump MK2 System 12V Attwoods shower sump systems deliver the performance youve been asking for. Choose from standard or large box sizes. They offer fast water flow into and out of the sump. The lid snaps into place to allow quick installation (and removal for cleaning) and includes a gasket to seal the sump box against overflow. The sump box even includes an air vent to prevent airlocks. It meets or exceeds all applicable standards of