Many older homes use an iron pipe as the water supply tube throughout the kitchen and bathroom. Today, copper pipes are the normal type of material being used. Iron pipes are notorious for rusting through or corroding. When this happens, they need to be replaced. Sometimes the right sized iron pipe cannot be matched, so an adapter must be used to attach a two inch iron pipe to a three inch pipe.
Step 1 - Position Adapter onto the 2 Inch Pipe
Wrap some plumber's tape around the threads of the two inch pipe. This tape is will eliminate any leaking caused by water coming through the threads. Twist the adapter onto the threads and tighten with an adjustable wrench or plumber's pliers.
Step 2 - Connect Pipes Together
Before connecting the two inch pipe to the adapter, you must also wrap it with plumber's tape. Connect the two pieces and tighten with the plumber's pliers.
Step 3 - Test Water
Turn on the water after the connection has been made to check if the water is going to leak through the pipe. If you notice a little bit of water dripping, you will need to tighten the nuts a little more. Use two pliers and turn one of them clockwise to tighten the connection.