In my bathroom I have had over the years continual problems with water backflowing up through the bath sink when draining the basin as well as the bath taking long periods to drain. Yes it has not been helped on occasions when slight blockages occur but I feel that its never been quite right at any time. I am at this time replacing the bathroom suite and want to try tp resolve that matter completely, the bath and basin share the same waste pipe which has a run of some 2 metres almost before it enters the main waste and as you can imagine there is a poor angle on the pipe. Would my best option be an in line non return valve placed just before the tee were the basin waste enters, or are there greater problems with these as I have been advised they need regular cleaning.