Soil pipe drop. Advice needed please.

[gordon115]

Hi everyone.
I am fitting a new downstairs toilet. However the soil pipe from the upstairs toilet is 4 meters away on the same wall.
How much drop will I need in cm?
For obvious reasons I don't want to get this wrong.
Thanks in advance.

 

[thomp1983]

40mm per 1.8m is what I used and the building inspector was happy with, over 4 metres that would be the far end 88.8mm lower than the start or in cm use 9cm

 

[gordon115]

Thanks Thomp1983. Exactly the advice I was looking for.

 

[Madrab]

Min in 18mm per m, max is 90mm, ideal is somewhere in the middle to ensure it is self cleaning.

 

[Agile]

I seem to recall it should be 1:40

If it is too steep then ( surprisingly ) the solids are not washed along the pipe.

 

[Hugh Jaleak]

1:40 is the rule of thumb for a 4" (110mm) pipe. Gives a 'Self Cleansing Velocity for the flow, as above. Theory is, too steep and the water runs away leaving the solids behind, too shallow, and the solids stay behind whilst the water seeps away.

In practice, half a bubble on a Metre spirit level should suffice.