27th Jan 2012, 10:44 PM
I'm dealing with a bit of flooding issue (surface water in the backyard & under the house) which I want to get rid of. However my block is flat. In fact, I suspect the back is actually lower than the front. So I'm investigating whether I can dig a trench next to the side fence and drain the water out. So my question is what is the minimum fall I need for different types of drains? E.g. Ag pipes vs Storm water pipes. Storm water pipes are smooth, therefore I assume it requires less fall. But I read articles online that Ag pipes needs only 1% which to me seems a bit low. Can a plumber confirm what is the general rule of thumb?