Soil Gradient

[IanNE]

I need to run a 13metre length of soil pipe, that toilet and sink will run into.
What gradient do I need for this horizontal run from the new manhole I'm fitting into the existing manhole 13 metre away..

I read somewhere 1:80 to prevent things getting stuck then other information advised 1:40??

Thanks

 

[noseall]

Somewhere between the two.

The industry standard has always been 1:40 meaning 25mm of fall every metre.

However the drains will still run with half this fall as long as they are arrow straight, uncluttered full plastic lengths and are laid to nanometric precision.