Ive just fitted a part 2 valve to my flats c/w tank but I am still getting a fairly constant drip coming from the plastic exit spout.Any explanations. Also I found it difficult to seal the union between the c/w pipe & the threaded opening of the new valve. I noticed on the old assembly that the inside of the threaded inlet was bevelled , should I have inserted some sort of rubber/fibre washer at the union nut. Thank you.