I am trying to connect a replacement shower and am having trouble with the water inlet connection. The shower is a standard Gainsborough model from B&Q. The inlet point on the base of the shower unit has some kind of plastic locking valve. I have tried connecting this to the hose supplying the water with a short length of copper piping then covering the join with plumbing sealant, but the connection leaks when the water is turned on. Any advice on how to make this properly sealed?