Drainage The first thing I have found strange is the constant requirement for testing at every stage but here with the building being largely wooden it does make sort of sense . A minor fault in the plumbing could lie undetected otherwise within the walls and only surface once damp damage had become extensive and be very costly to repair . Thus it is required that once the drains have been run throughout the building frame they are filled completely with water to ensure their soundness . I took the wise precaution of making up a screw in fitting with a pressure gauge and an inflation valve to test the pipes with air first as once the system was full of water it would be time consuming and difficult to get the water out and to dry where necessary to effect repairs . First things first - all the drainage flows within the house in a trunk and branch layout . The main 4 inch drain had already been tested and laid under the basement floor . There are tables to show how