| 摘要 |
A liquid drainage system comprising, a receptacle having a chamber to receive liquid, and a depending annular wall defining a valve seat at a lower portion thereof and an opening in the region of the seat. The system has a valve element comprising a sheet of flexible relatively stiff material being sufficiently large to extend across the opening and sealingly engage against the seat peripherally around the wall. The system has a device for retaining a central portion of the valve element adjacent the seat.
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