I wish to install 2 radiators to a newly built conservatory and luckily the main 3/4inch pipes from the boiler are conveniently located. I plan to connect plastic 1/2 pipes to these using compression fittings. how does the plastic pipe (i think its called qualpex) fit into a brass compression joint? Does it need a copper olive ring and insert? Secondly, how does copper piping fit into plastic fittings? - do you just push it into the o ring and metal "gripper" which came with the fitting?.