Plumbing for Homeowners Guide
Understand your drain plumbing with this free guide on plumbing for homeowners…
While this guide does not specifically cover greywater plumbing, it does cover key plumbing relationships such as the critical distance between a drain and a P-trap (otherwise called the horizontal length of trap arms), the elevation relationship between a P-trap weir and the fitting that connects it to a vent, correct venting of drain pipes and their P-traps, and required pipe diameters based on drain-water source.
Remember that a three-way valve (enabling you to direct drain water either to the sewer/septic line, or to the landscape) should installed downstream of the drain’s P-trap and vent.
A greywater line should also always be upstream of any blackwater flow, e.g., the water from a toilet. This is because if any blackwater mixes with greywater, then all the water becomes blackwater, which is far dirtier and more difficult to manage than greywater.
Blackwater drain pipe from toilets is usually 3 inches (75 mm) in diameter, while drain pipe from greywater sources, such as bathroom sinks or showers, is usually 1.5 inches or 2 inches in diameter.
Greywater-collection plumbing consists of all the drain pipe in a house that is connected to the greywater pipe that exits your house and connects to the greywater-distribution plumbing/irrigation line (outside your home) in your landscape.