Gasket for the Nipple-Nut Kit. Installing the nipple-nut kit on the polyethylene tank: Required parts: – FE nipple kit + nut + FI plug. – gaskets for the FE connection (2 pcs.) – seal the inside and outside of the tank wall. – gasket for the FI plug (1 pc.) – allows sealing when the plug is used to isolate the connection.