How Does Kitchen Plumbing Work, and Why Is It So Complicated?

March 11, 2020

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Kitchen plumbing is often more complicated than homeowners realize, which is one reason to leave plumbing installation and repairs to the pros! Even the smallest kitchen plumbing task, such as replacing a sink or faucet, can take hours and, if performed improperly, might risk water leaks and other such damage.

Kitchen plumbing fixtures are attached to a home’s water supply system, as well as its drain-waste-vent (DWV) system. The water supply system brings water into the home while the DWV system removes water and waste, and provides vents for creating air pressure and releasing or blocking sewer gasses.

While many homeowners might have a cursory knowledge of a home’s water supply system, these connections are still quite complicated and need expert repairs and installation. Overlooking repairs or parts for the home’s DWV system also risks water leaks, sewer gasses making their way into the home, and eventual clogs.

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To ensure you keep your home’s kitchen plumbing in good work order, and know when to call a professional plumbing company near you as needed, note some vital information about your kitchen’s fixtures and features. It’s also good to consider calling a plumber if you have any doubts about your home repair expertise, so you avoid making needed repairs worse or causing damage during your DIY installation attempts!

How Does Kitchen Plumbing Work?

To better understand kitchen plumbing, consider some basics about its design and overall function.

  • First, note that kitchen and bathroom plumbing are similar but still different in many ways. Don’t assume that repair advice for bathroom sinks applies to kitchens, and vice versa, or that a bathroom sink can be installed in a kitchen! For example, a kitchen sink is designed for connection to added features not found in a bathroom such as a water filter, garbage disposal, and dishwasher.
  • A kitchen sink drain is fitted with a strainer, to capture and slow down food disposal. This strainer is typically designed with a gasket that is fitted to the sink drain with a bit of plumber’s putty, to keep it in place and provide a watertight seal.
  • The strainer body ends with a tailpiece, connected to the gasket with a locknut and to the sink’s pipes with a threaded coupling or connector.
  • The rounded pipe you see under a kitchen sink is called a trap. This trap is purposely rounded to hold standing water, which blocks sewer gasses from coming up through the connecting pipes and to the kitchen sink. Every time you turn on the sink, that standing water is replaced.
  • The trap is also rounded to slow down the flow of water through the sink pipes. Water helps move solid waste along and, if water flows too quickly, it won’t have a chance to wash away that waste. In turn, solid materials might build up along the inside of the pipe and clogs would then form.
  • The trap is connected to pipes with what’s called a slip-joint coupling. This coupling is designed purposely for easy removal, to address clogs along the trap. Some traps even have what’s called a clean-out plug at the bottom, so you can release clogged food particles and other items without having to remove the trap itself.
  • If your kitchen sink has a garbage disposal, this piece is connected to a special strainer body above the trap.
  • Kitchen sinks also have valves, usually one for hot water and one for cold water. Older homes might have just one valve. It’s good to note the placement of these valves in case you need to shut off the water supply to the kitchen for any reason.
  • Some sinks might have an additional saddle valve, often for a water filtration system, instant hot water tap, and other such add-ons.

What Is Venting and What Happens If You Don’t Vent Plumbing?

Most homeowners know that plumbing must be connected to the home’s water lines, to bring water to fixtures and features, and to the home’s drain lines, which take away water. However, many don’t realize that plumbing pipes need vents, to bring fresh air into pipes and release air from drains as well!

Without proper venting, water often drains slowly, increasing the risk of clogs and backups. You might also notice more dirt and debris clinging to the inside of sinks and tubs with slow drains. If sewer gasses leak into the home, you’ll notice that unpleasant smell rather quickly, while methane gases from sewers are dangerous and even downright deadly!

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Most plumbing vent pipes go through the home’s roof, allowing air to rise quickly and vent away from the residence as much as possible. In some cases, different fixtures might share a vent but local building codes dictate plumbing venting, including the location of the vent piping, its size, and the like.

Proper venting is one reason to leave plumbing repairs and installation to professionals! Improper venting is one common reason for DIY repairs and installation to fail a plumbing inspection and for resultant clogs, gurgling water, unpleasant odors, and the like. Hiring a plumbing company near you ensures your repairs and installation are done correctly and that the plumbing will work as expected.

Where Should a Sink Be Placed in a Kitchen?

If you’re considering a renovation project for your home, it’s best if you have a plumbing contractor manage the kitchen plumbing installation and relocation for you. He or she will ensure all pipes and fittings are connected properly and vents are not compromised. If you do want to tackle this job on your own, note a few considerations about the location of the kitchen sink:

  • A kitchen sink, stove, and refrigerator should form an L or U shape, and sit no more than 10 feet away from each other, for maximum convenience. Placing any of these items further apart means more walking back and forth between them for meal prep and cooking.
  • Consider average winter temperatures in your area and note that pipes located along outside walls are more likely to freeze than those running along an interior wall. In areas with harsh winters, note if you can relocate the sink so that its pipes run down an interior versus an exterior wall.
  • While locating pipes along an interior wall can mean less risk of them freezing during wintertime, it’s also good to have a window over the kitchen sink, for a nice view when washing dishes! If you do move the sink to an interior wall, be sure to consider the number of windows in the kitchen and reconsider covering one with the refrigerator or cupboards, to avoid a dull and unwelcoming look.
  • Also remember to note local building codes when moving a kitchen sink. Typically the pipe under the sink must be placed a certain number of inches away from the wall, for accessibility and to ensure connected pipes are large enough to accommodate water flow. Before moving a sink, be sure you accommodate those requirements without the sink getting in the way of foot traffic or a door.

Are All Kitchen Sink Drains the Same Size?

Local building codes dictate the size of a kitchen sink drain but note that most are 1-1/2 inches to 2 inches in diameter. Sink drain openings are always 3-1/2 inches in diameter; this is the industry standard.

Sink basket strainers are all the same size, 3-1/4 inches in diameter. This 3-1/4 inch basket assembly fits drain openings of 3-1/2 inches so there’s no need to measure for a new basket strainer. However, there are different types of sink basket strainers; some will have a full assembly with a ring nut and basket while others have install rings attached, for easier assembly.

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If you’re measuring your kitchen sink drain for a new basket assembly, it’s often good to take the old part to a hardware store and buy an identical replacement. This will ensure you get exactly the part needed for your new sink drain and will avoid improper fittings and potential leaks.

Why Are S Traps Illegal in Many Areas?

Most homes today are fitted with a P trap, or a pipe with one curve, like the letter P sitting on its side. An S trap has an additional curve, usually going up from the end of the P trap. These traps are often illegal in many areas as the S design runs the risk of siphoning water from the bottom of the trap.

Without standing water in the trap, sewer gasses and even vermin might make their way into the home. In many areas, S traps are now illegal to use for plumbing, meaning a home won’t pass inspection with S traps installed under the sinks. You might still be able to buy S traps at a home improvement or hardware store as they’re sometimes used for drains without vents.

If your home has S traps installed currently, you might contact a plumbing contractor near you about updating the kitchen plumbing. A new P trap means less risk of sewer gasses entering the home and less risk of your home not passing inspection after a renovation or when you’re looking to put it on the real estate market!

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