Abstract: A tank seal for use in cast concrete walls has a generally cylindrical main body portion with a stepped outside wall having first axially-extending portion, a second axially-extending portion having an outermost diameter less than an outermost diameter of the first axially-extending portion, and a radial ledge or step separating the first and second axially-extending portions. A wiper blade portion extends radially inwardly of the stepped outside wall, from an end of the second axially-extending portion opposite the radial ledge, terminating at a third end. A circular membrane or web extends across the third end, including at least one annular groove therein to facilitate removal of at least one circular portion of the web. The radial ledge collapses and the first axially-extending portion puckers in response to compressive force exerted on the tank seal in an axial direction, reducing the axial length of the tank seal.