fiddly shower waste problem

[oharaf]

We have installed a shower under the stairs. No problem

What I would like to know is can I use a reducer and narrow waste pipe i.e. about 20mm (ish) to route the waste outside. Access for standard waste is very difficult due to the space.

What degree of drop will I need to ensure good drainage?

ANy advice would be very welcome

Would post a diagram but don't know how to[/img]

 

[markplumb]

shower waste should be 40mm. go down to 32mm and most people will start getting problems unless it's a very short run. general rule is a drop of 1:40.

you can reduce the pipe down to 20mm if you were to use a pump like saniflo. http://www.saniflo.com/products/sanishower.asp as you can see from that pic you can run the waste up vertically if you need to.