Every bathroom remodeling project inevitably involves dealing with bathroom plumbing. Whether you're completely gutting a bathroom for a total makeover or simply replacing the flooring material, you'll need to remove and replace plumbing fixtures such as the toilet, disconnect and reconnect water supply pipes, and often much more.
Before you begin any work that involves plumbing, it is very important to understand how the plumbing system works, what's involved in making various types of improvements and repairs, and--in some cases--how to handle some jobs yourself.
Two separate plumbing systems serve a bathroom: the water supply system and the drain-waste-vent (DWV) system. The water supply delivers clean cold and hot water to all of the fixtures--sinks, shower, tub, and toilet. The DWV system sends waste water to the sewer or septic tank and exhausts sewer gasses through vent pipes. To prevent tainting water in the supply system, there is never a direct connection between these two systems.
See the drawing for a closer look at the supply and drain-waste-vent systems. Note that the cold-water supply pipe serves the tub, shower, sink, and toilet. The hot-water supply pipe doesn't connect to the sink, tub, and shower. Most modern bathrooms employ a pressure-balance valve to prevent scalding in the shower.
--Don Vandervort
