My house is about 40 years old and is in Kidderminster. I've developed a small leak where the water main comes into the house and through a concrete floor in a downstairs loo. I have dug down on the outside of the wall to the water main and was surprised to find it black plastic with 22mm diameter. I have spoken to people like Polypipe who tell me it would normally be 20 or 25mm and blue. I now want to put a straight coupler from the old to the new pipe, but cannot find a suitable 22mm push-fit coupler to go underground. Is it OK to use a standard 22mm compression coupler? (With pipe inserts of course).