Plumbing Basics

Residential plumbing systems are easy to understand. In general, a home plumbing system consists of two networks of pipes. One is the supply system—the pipes that carry water into the house and distribute it to fixtures. The other is the drain, waste, and vent (DWV) system, which carries drain water, waste, and harmful gases out of the house.

Supply

In the supply system, an underground line from a water source connects to a meter that measures the amount of water entering the house. Next to the meter is a shutoff valve that, when closed, stops water from flowing into the house. The main supply line branches into two lines—one for cold water and one for hot. The cold-water supply line feeds the network of supply pipes throughout the house. The hot-water supply line goes to your water heater. From there, the hot-water pipes run parallel with the cold-water pipes to serve various fixtures and faucets.

Drains and Vents

Your home’s water-supply system is pressurized, but the drain-waste system depends on gravity. These pipes also are connected to vents which allow sewer gases to escape harmlessly up a chimney-like vent stack. Because each new or moved bathroom fixture must connect with a stack, you must know the locations of your main vents, then determine a route for attaching new vent lines to them. Consult local building codes for the required size and general confirmation of drainage, waste and vent lines.

Key Points
Replacing old fixtures with new ones in the same location is fairly simple. But it’s best to leave more complex plumbing jobs to a professional unless you’re an accomplished do-it-yourselfer. Either way, you should be aware of some basic rules and principles:

Each bathroom fixture must have a drain with a trap - a curved pipe that always retains a little water in it as a seal to prevent sewage gases from getting into the house.

Each drain must be connected to a vent pipe that either goes directly up through the roof or connects to another vent stack. Plumbing vents run from the lowest part of the system clear up to the roof. For cosmetic reasons, it’s best to run vent stacks up through the back side of the roof, not the front.