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The Anatomy of Your Kitchen Sink Plumbing


Understanding your kitchen sink’s anatomy can help keep it running efficiently. Knowing its parts will enable you to spot potential problems early and save yourself costly plumbing repairs in the future.

Installing a double sink may necessitate lowering the position of a sanitary tee fitting connecting to the drainpipe in the wall, and this can be an extraordinarily complex and time-consuming task.

Water Supply Line

House water supply lines (commonly referred to as cold or water service lines) bring fresh, clean water from outside into the house for distribution to faucets inside. They may be constructed of copper, plastic, or galvanized steel and come fitted with various fittings that facilitate distribution.

Water lines that lead from sink drains to the house’s water heater then heat the water for household consumption, with typically shorter pipes to minimize heat loss during transit.

Kitchen sink water lines also connect to a home’s drain-waste-vent system for draining away its wastewater, so they must slope downward as they leave the drain, with their tailpiece facing in the right direction so as to avoid entering living spaces with sewer gasses. In addition, check that your “trap” has water in it – this helps avoid foul odors being released into your kitchen from empty or clogged traps.


Faucets serve as the interface between fresh water and wastewater in your sink, usually attached either directly to it or the wall and available in various styles and finishes. Faucets typically feature one or two handles or levers to control the flow and temperature of water, as well as colors or designs to add personality.

If you were a water molecule floating through your sink and saw the faucet, the first thing you’d likely notice would be its small circular opening and rubber stopper secured by a screw. On the other side of that opening is another screw, which acts like a wedge to block water molecules until you decide to pass through.

Mounting hole size and spacing are other features that can have a visual impact on a faucet’s look. Before buying one, take measures of your sinkholes to make sure they align appropriately; otherwise, you could run into issues during installation.


The P-trap under your sink is an essential plumbing device that serves a vital purpose. This curvaceous pipe (some might argue more like an S or X, but let’s avoid an alphabet war here) traps noxious sewer gasses from entering your home by trapping them in its curvature and inside its curvaceous interior walls.

At its heart is a water seal created at the weir, which ensures freshwater enters via every flush from your sink to maintain this seal. In every use of your sink, wastewater flows into the trap to replenish its curve with freshwater, maintaining this water seal and the system’s proper functioning. If you suspect your drain line is blocked up, the first place to look should be the P-trap. An obstruction may be in its bend at the weir, and using a drain cleaner or snake can quickly clear away obstructions within this bend, from which drain cleaners or snakes should be able to unblock it.

Unfortunately, your little hero is not indestructible – over time, the water in your trap may evaporate, leading to sewer gases creeping into your drains and foul stench filling them up with an unpleasant stench. Thankfully, fixing this issue is relatively simple; pour a gallon of water down your sink drain in order to restore water seal and restore sealage.


A drain tailpiece, consisting of a short vertical length of straight pipe, connects the sink strainer to the drain. A side outlet on its tee fitting accepts waste pipes leading from garbage disposals or sink basins, while its bottom outlet leads directly into a trap for the disposal of wastewater.

U-shaped trap bend and J-shaped trap arm are two critical elements of your sink’s drain trap, designed to prevent sewer gases from entering through its drainpipe and entering your kitchen via your sink drain. Ideally, the top of each arm should slop downward by approximately 1/4 inch per foot towards a branch drain pipe located behind your cabinet in order to connect to an appropriate branch drain tee fitting in the wall behind the sink cabinet.

P-trap tailpieces connect to sink drain vertical tailpieces using slip nuts, which are threaded couplings that can be tightened or loosened using channel-type pliers, making these connections watertight and durable. To replace sink drains quickly and easily, coat both ends of the new tailpiece and tee fitting with PVC primer before installing them.

Drain Pipe

Though kitchen sink plumbing may appear complex, installation is actually straightforward when following some specific steps. Many homeowners opt to do it themselves instead of hiring a plumber as this can save money; it is, however, vital that you understand the anatomy of your sink before starting installation.

The drain pipe connects the P-trap to your home’s sewer or septic tank system and transports waste away from sinks while also helping regulate air pressure to prevent toxic fumes from backing up into your house through drains.

Kitchen sinks often include more features than just a faucet and drain, such as a garbage disposal and dishwasher. Water supply lines and drain lines tend to be combined so as to accommodate these additional appliances.

Before installing the plumbing for your kitchen sink, ensure that its drain outlet height is low enough to accommodate these extra features. Depending on the size and depth of your drain, this may involve lowering its position relative to its sanitary tee in the wall.