Shower waste with long run

[nimh]

I am fitting a shower and have been given contradictory advice by two plumbers. One says run it in 40mm and one says run it in 50mm.

From the shower waste is 1m to to the first vertical drop of 100mm. The next run is 3.5m to the next vertical drop of 2m into a WC waste.

What fall would I need for the 3.5m run?

Clearly 50mm is better than 40mm.

Is 40mm sufficient for the whole of the run?

 

[mysteryman]

Minimum fall should be 1 in 40, which is an inch per metre. 40mm should be plenty big enough. You should provide rodding access, easily done using swept tees with rodding eyes at some of the bends.

 

[yerino]

40mm should be big enough but if it doesn't cause anymore problem you might aswell run it in 50mm.

As stated above try and put in a rodding point somewhere accessible.

Obviously the more of a fall the better as shower wastes can easily blocked up with hair etc.