iv done this myself there should be two black peices
one large with two holes where the pipes go and a smaller peice and a small spring the first thing you have to do is put the large peice in clipping in from the bottem it is hard to get in and you may need a screwdriver to help prise it in once that is in the other end should just slot in the small black peice should go in easy theres a hole on each end you may need your screwdriver again once this in done just put the spring in if you still have trouble with it i can send you some pix's showing you how to do it
dave
dave, July 2008