Copper pipe connecting to plastic valve leaks?

try putting the ptfe tape, between the brass nut" and the olive"on the brass nut side of the olive, put a good bit on , keeping it tight , put some on the plastic threads as well , the plastic threads might be half inch, and the brass nut ,is 15mm. you can still get a brass /copper ballcock . with 15mm , but it will have to fit into the cistern, and be able to move up and down ,with out it getting stuck in the body. that will work no problem if its fits, B&Q, or any hardwear..

l
April 2011