When connecting the reducing tee pipe fitting, the flange pipe fitting and the connecting part of the pipe fitting shall be connected to the pipe end.  There are holes in the flange and bolts hold the two flanges together.  Gasket seals between flanges.  Reducing tees are pipe fittings with flanges.  It can be cast, threaded or welded.  Reducing tee connection consists of a pair of flanges, a gasket and a number of bolts and nuts.  The gasket is placed between the two flange sealing surfaces, and after tightening the nut, the specific pressure on the surface of the gasket is deformed after reaching a certain value, and the uneven place on the sealing surface is filled, so that the connection is tight without leakage.  Flange connection is a detachable connection.