If your DFU is drainage fixture units all you need to know is the following.
1 GPM pumped drainage (continuous flow) is considered an FU
A three square feet of roof drainage is also considered a fixture unit
When combining a drainage and storm system you must do interpolation to properly size the piping.
Some codes also go by pitch of pipe to allow more or less FU’s and venting fixture units if properly sized also take developed length into consideration. All of these can be memorized with just a little effort.
» This message has been edited by Lorenzo on 17 September 2001