We propose if galvanized pipes are current, you think about having them replaced by a qualified plumber. Future, simply just drive the pipe in the fitting until finally it reaches the end. The O-ring or gasket In the fitting will produce a tight seal, securing the connection. Push-in good shape https://www.malleableiron-pipefitting.com/industry-knowledge/how-to-connect-non-threaded-galvanized-pipes.html