It is sometimes necessary to test a drainage system in sections, so as not to delay the completion of other parts of the work. When testing in sections, all parts of the drainage system should be subjected to at least one test under a hydrostatic head of ten feet or more. When a house drain is installed and is to be covered it can be tested by first extending all branches above the cellar floor level and plugging all outlets but one, into which is calked two lengths of pipe, then filling the system with water until it overflows the top length. When the soil and waste stacks are afterwards installed and tested, the entire system is filled with water, thus subjecting all parts to at least one test.

When soil, waste and vent stacks are installed first, they should be extended down below the basement ceiling, and they may then be tested separately or collectively by connecting them together with small sized wrought iron pipe. After the house drain is installed, the system should then be filled with water to at least ten feet above the highest untested joint in the vertical stacks.

A good plan to follow where testing drainage systems in buildings from four to eight stories in height, is to fill and test the work as soon as it is installed. By so doing, any serious leaks in the pipes are discovered, and if necessary to remove a defective section it can be done with much less effort than after the stacks are through the roof and lead roughing in place. Furthermore, workmen are more careful when they have to test their own work immediately after installing it.

The drainage system in extremely tall buildings is tested in sections, so that no part of the system will be subjected to excessive pressure. This is done by leaving out a short connection of pipe between the several sections. Then, after the several sections have been tested separately, beginning at the top, they are all connected together. When the top section has been connected to the one next below it, the stack is filled with water to a height of 10 feet above the connection. This double section of pipe, after being emptied, is then connected to the section next below it, and the stack filled with water to 10 feet above the connection, as in the former case. This operation is repeated until all sections of the drainage system have been connected, and the joints of all connections subjected to a test.