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Plumbing Basics – What You Need To Know

Plumbing Basics - What You Need To Know

Plumbing Basics – What You Need To Know

Plumbing works on the simple concept of “water in — water out.”

In a new home, the plumbing system features three main components, the water supply system, the drainage system, and the appliance/fixture set.

Plumbing Basics – What You Need To Know

In most communities, to install plumbing, you must be a licensed plumber, or you must work under a licensed plumber who approves and oversees your work. Local codes determine standard plumbing procedures, but a new home’s fixture placement, pipe routing layout, and pipe size depend on the home’s design.

Installation Timetable

Sewer accommodation stubs are set before pouring the concrete foundation, but the bulk of the plumbing takes place later. The rough-in plumbing phase, which occurs in conjunction with the wiring and duct installation phase, takes place after the framing is complete, but before hanging drywall. This is the time to install main drains in floors and connect them to the stack. Rough-in drain fittings install now for sinks and tubs. This is also the time to install water supply pipes or tubing and set toilet flanges.

Plumbing Fixtures

Because they’re often too large to set once walls and doorways are framed, tubs and tub/shower units are typically set before framing the walls. Since a lot of construction has yet to take place, cover these fixtures with cardboard or even old blankets or rugs to protect them from scratches. Set and connect sinks and commodes last, after finishing the walls and laying the flooring.

Water Supply System

The main pressurized water supply line enters the house below the frost line, then splits into two lines; one provides cold water, and the other connects to the water heater. From there, the two lines supply hot and cold water to each fixture or appliance. Some homes have a water supply manifold system featuring a large panel with red valves on one side and blue valves on the other side. Each valve controls an individual hot or cold tube that supplies water to a fixture. Using a manifold system makes it simple to shut off the supply of water to one fixture without shutting off the water supply to the whole house.

Drainage Pipes

The main vent-and-soil stack, which is typically 4 inches in diameter, runs vertically from beneath the ground floor to above the roofline. Waste drains connect to the stack, directing waste downward to the main sewer drain, which then exits the home below the frost line and ties into the municipal sewer system or runs to a personal septic system.

Vent Pipes

Without a constant source of air, water locks can form in drainpipes, causing clogs. All drains require ventilation, but a single vent, usually installed behind a sink, can serve additional fixtures and appliances that connect within 10 feet of a standard drain line. Vent pipes, which are 2 inches in diameter, connect to the vent-and-soil stack in the attic. When a fixture sits too far from a common vent, it requires an additional vent pipe, which connects to the stack or exits the roof separately, depending on the home’s layout.


A drain trap is a U-shaped pipe that connects to the bottom of a sink, shower or tub drain. A trap retains a small amount of water that prevents smelly sewer gasses from backing up into the house. All plumbing fixtures require drain traps except the commode, which comes with an internal trap in its base.


This Old House: From the Ground Up: Plumbing

About the Author

Glenda Taylor is a full-time writer with work featured in national and international publications. Taylor, a residential contractor, specializes in new construction and remodeling writing. She is also the category manager for eHow Now’s expert Handyman channel. Taylor’s formal education includes marketing and a bachelor’s degree in journalism.

  1. I typically like to hire a plumber to come and take care of any plumbing needs that my family may have, but I thought it would be good to do some research on how things are done just in case. I did not know much about vent pipes before reading this. I will look and see if I can find mine behind the sink!

    • Erika….more than likely you have a vent at your sink. If you don’t it usually likely you can add a new gadget called an Air Admittance Valve somewhere on the sink drain (also called an AAV). As a kid you may have put a straw in a glass of water and ut your thrumb over the end of the straw so the water would not come out of the straw. When you took your thumb off the water would drain out. This same theory applies to your drainage system. If your drain pipes cannot get air you can get drain lock…thus the reason for plumbing drainage system venting.

  2. Very helpful article. Do all plumbing fixtures require a water supply and a drain? Is it up to code to install a fixture without a water supply (ie. Drain only) or a fixture without a drain (ie. Supply only). Two plumbers said 2 different thinks and I was hoping to get the facts straight.

  3. Wow, this article on plumbing basics is super helpful for those of us who aren’t exactly experts on the subject. I love how it breaks down all the different parts and functions of a plumbing system in an easy-to-understand way. I definitely learned a lot and feel more confident about tackling some basic plumbing issues around my home now. Thanks for sharing!

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