A patented mechanical compression seal used to shorten the PC/PET RetroDrain. Tough nylon flanges and stainless steel screws provide the necessary strength torque and to compress the EPDM rubber gasket. The seal is activated by tightening the internal screws with the U-Flow screwdriver. This compresses the thermoplastic seal, forcing it to expand and make contact with the wall of the old pipe, thus preventing vertical movement and stopping water backup damage. This design feature is incorporated in all UFlow retrofit drain products. Available in 3", 4", 5", and 6" sizes.