Patent ID: 7178686

Claim:
A subterranean tank assembly for storing liquid below grade, said tank assembly comprising: a vessel having a vessel wall of molded synthetic resin material defining a liquid-receiving chamber therein and at least one portal projecting generally upwardly from the vessel wall and presenting an opening for gaining access to the chamber, said portal including a rim having a substantially horizontal circumferentially extending closure surface in surrounding relationship to the opening and an inwardly tapering receiving surface; a cover of synthetic resin material; and a riser of synthetic resin material for coupling to and elevating the cover to a position at or above grade and positioned intermediate said rim and said cover, said riser being substantially tubular and presenting a normally upright longitudinal axis and including a normally bottommost connector portion adapted for coupling to said rim, said connector portion also including an inwardly tapering surface complementally configured for mating with said receiving surface of said vessel in sealing engagement, a normally topmost connector portion adapted for coupling to said cover, at least one continuous and uninterrupted cylindrical riser wall, and a plurality of axially spaced continuous and circumscribing ribs positioned radially outward of said riser wall, each of said ribs including a pair of substantially horizontal flanges radially oriented in a plane transverse to the longitudinal axis of the riser and connecting said ribs to said riser wall, said flanges each being complementally sized and configured relative to said rim whereby said a circumscribing cut through one of said ribs or said riser wall adjacent said flange will reduce the longitudinal length of said riser and whereby the remaining, normally bottommost flange of the riser may be coupled to the rim in sealing engagement.