Effective drainage systems

An effective drainage system must be able to self clean to ensure the wastewater passes freely through the system to the authority sewer. This is achieved by ensuring wastewater travels with sufficient velocity through the pipework. Velocity is determined by a combination of gradient and pipe diameter.

A small diameter drain will give a greater depth of water in the pipe. This results in a greater velocity of water flow than a large diameter drain carrying the same volume of water. The faster flow of water will ensure solids are not left behind in the pipe.

Drains operate most efficiently when the ratio of the liquid to air in the pipe is 65:35. This ensures adequate ventilation through the system and allows drains to flow at a rate to allow them to self-clean. You must accurately size sanitary drainage systems to ensure the 65:35 ratio is maintained.

Graphic of a house showing pipes from the toilet and laundry, each with a ratio of 65:35 liquid to air. A vent leads off from the laundry pipe. Both pipes join and enter the sewage drain.