Can I ask what is the minimum drop for drains? We are looking to move our bathroom upstairs and the easiest option is to drop the waste from the new loo, down through the lounge corner into the cellar, across into the old waste pipe where it exits the house and runs into a drain outside. But it is a fair distance in the cellar, approcimately 4m then a 90o bend and another 8m. What would be the minimum drop and whats the best way of measuring it? Do I need to buy a laser level?