This valve is installed on the RO holding tank to isolate the tank for servicing the RO. This valve has a 1/4″ female pipe thread to install onto the tank and 3/8″ quick connect for the tubing from the RO. Measure the outside diameter of the tubing connected to your old tank to determine if this is the correct size. To install the valve first clean the threads on the tank, nest wrap teflon™ tape around the threads 3 times, then carefully thread the new valve onto the tank making sure not to cross the threads. You should be able to turn the valve easily 3 times before it starts to give resistance. Tighten the valve a total of 5 turns. do not over tighten the valve onto the tank, it will damage the valve.