Patent ID: 7155751

Claim:
A drainage closure for an upwardly-directed circular valve seat in the bottom of a water tank, said closure being so proportioned as to close said valve seat when in full contact therewith, and to permit flow past said seat otherwise, said closure consisting essentially of a hollow body having a central axis, a substantially constant dimension of wall thickness throughout, a dimension of axial length, an upper neck, a lower guide, and an enlargement between said neck and said guide, said neck and guide being coaxial, an upper and a lower surface on said enlargement, said lower surface facing said valve seat and being so dimensioned, disposed and arranged as to close said seat with said lower guide extending below said seat, the neck, guide, and enlargement forming a continuous passage open from the upper end of the closure to its lower end, the enlargement providing buoyancy for the closure when it is vented at the neck and guide when both of said surfaces of the enlargement are immersed in water in the tank.