Im not sure if I have explained fully enough.

Where the Washing machine is going, the obvious way is to fit a 'Stand-Pipe' behind the machine, then round a Swan-Neck type bend before heading off towards the Main House Drain, which is about 2 Metres away.

I havent really thought about how the machine will connect to the Drain Pipe yet, not really worried about that at this stage.

Most people would probably take the pipe out through the wall and along the outside wall into the drain. However, I dont really want the pipe on the outside wall, so I want to run it under the floor. However, there isnt alot of height available under the floor where the pipe is going, so I need to chase a channel out for the pipe to run in. Thats why I need to know about Fall on the pipe as the more fall that is needed, the deeper my Channel will need to be.

Make more sense now?