The biggest single factor determining the ease, practicality, and expense of a basement bathroom installation is the height at which the house's main drain pipe exits the foundation wall. Since this pipe must run slightly downhill from the house, the height of the sewer or septic system will determine the height that the pipe exits the basement. With a sewer, the height is predetermined by the depth at which the town or city installs its drain system. With a septic tank or cesspool, the height is generally determined by the height of the existing water table. If your client is one of a lucky few, the drain pipe will exit at a level below