The Parts of the Plumbing of the Bathroom Sink

The Parts of the Plumbing of the Bathroom Sink

Are you overwhelmed by the plumbing of your bathroom sink? You’re not alone. Whether you’re a novice looking for an introduction or an experienced homeowner needing a refresher, this blog will provide you with the key components of a sink to help you understand and troubleshoot your own system. Let’s take an approachable dive into the parts of the plumbing of the bathroom sink.


The drain of a bathroom sink is responsible for quickly and effectively carrying wastewater away from the sink itself. The assembly is comprised of multiple components to help ensure a proper seal between your sink and the drain line. The main parts of a drain assembly include the strainer, waste elbow, tailpiece, trap arm, P-trap, and trap adapter.

  • Strainer – The strainer is a protective covering which fits over the top of the drain opening that helps to prevent items such as jewelry or soap scum from being washed down the drain.
  • Waste Elbow – The waste elbow is an elbow fitting which connects the bottom of the Tailpiece at an angle to allow for water to travel more freely away from the sink base.
  • Tailpiece – Also known as the connecting tube, this long piece runs horizontally out of one side of the strainer body into another branch or fitting. This is often used in cases where there isn’t enough space above or below your sink for all connections to be made into one single bin-filling location.
  • Trap Arm – A curved tube connected to both ends at different marking points so that it can direct water out of one side and into another’s pathway. This prevents dirty water and debris from seeping back up into your sink after it has already been washed away by moving down the drainage system and out through an exterior vent stack pipe outside your home’s walls.
  • P-Trap – This portion is a bend in a pipe that runs directly under and parallel with your sinks’ basin, forming a “P” shape by connecting two separate pipes together tightly with connectors known as j-bends or slip rings on either end so that wastewater can pass through without any obstruction whatsoever while maintaining its tight seal at all times.
  • Trap Adapter – This fitting wraps around every joint in order to ensure its secureness within each element as well as prevent any leaking or clogging issues from occurring over time due to aged materials or improper placement during installation process.


The “P” in P-trap stands for “plug“. The trap assembly is an essential part of the bathroom sink plumbing. It attaches to the bottom of the sink, curving downwards and connecting to a straight pipe that runs horizontally underneath the sink.

The P-trap creates a seal between two pipes that prevents bad-smelling gasses and sewer insects from coming up out of the drain and into your home. It also connects directly to the wall outlet drain, which ensures that water won’t drain out of your sink when it’s not in use.

The P-trap will typically be made of

  • PVC (polyvinyl chloride)
  • ABS (acrylonitrile butadiene styrene) plastic material

although sometimes metal is used as well.

Supply Lines

Supply lines are one of the most essential components of the plumbing of a bathroom sink. These pipes bring in fresh water from the main line to the sink fixtures, typically located on either side. Supply lines come in various lengths and sizes to fit all types of sinks. The two standard connection sizes are 3/8″ and 1/2″.

As such, it is important that you have the right size parts for your particular sink installation. When it comes to materials, supply lines can be made from copper tubing or flexible plastic tubing. You should also purchase a shut-off valve for each side; this allows you to stop water flow without having to turn off the main line’s shut-off valve.

Lastly, you will need two supply tubes with compression fittings, one for each side, connecting your sink faucets to the shut-off valves. These fittings make sure your pipes remain tightly connected despite changes in water pressure or other environmental conditions that could lead otherwise lead to leaks and damage over time.

Shutoff Valves

Shutoff valves, also referred to as stop valves or isolation valves, are usually located right under the sink and allow you to control the water supply. The two shutoff valves stand independently on either side of the sink, connected with a flexible hose. One shutoff valve controls hot water and one controls cold water; they are usually color coded red for hot, blue for cold.

To close these valves securely all the way, turn each knob clockwise until it stops entirely. It is important to remember to turn off these valves when you are doing any plumbing repairs on your sink or when replacing any of the parts in order not to flood your room.


The faucet is an integral part of the plumbing of your bathroom sink, usually mounted on top of the sink itself and accessible from afar. The faucet typically features two handles or one handle with a lever, allowing you to control the flow and temperature of your water independently. Generally speaking, one handle adjusts the water’s hot-cold ratio while the other is dedicated to turning it off and on.

Faucets generally consist of:

  • A base mounted on top of your sink
  • Two handles for water control
  • Two valve stems beneath each handle
  • A cartridge inside each valve stem that helps direct water flow

Depending on your model of faucet and whether it is a single- or double-handle design, there may also be some other metal parts found inside the base which are used to secure and connect all other parts together. In some cases you may also find aerators inserted into your faucet for additional water conservation measures.

Pop-up Drain Assembly

A pop-up drain assembly is an important component of a bathroom sink as it is responsible for draining water from the sink into the home’s plumbing. This component usually consists of two main parts: the popup stopper and the pivot rod. The popup stopper is designed to fit inside the drain pipe opening, whereas the pivot rod helps lift and lower the pop-up stopper in order to close or open it when necessary. It is also connected to a lever located on top of the sink which allows for easy access and use when needed.

The internal parts of a pop-up drain assembly include components such as a clevis strap, spring clip, tailpiece nuts, and overflow tubes; these are all designed to ensure that water flows properly through the system without any disruption. Additionally, some assemblies may be accompanied by other items such as washers and seals which can help prevent any leaks occurring in this area due to wear or tear with time.

In order to repair or replace your bathroom sink’s pop-up drain assembly properly you should first consult a professional plumber as there may be individual components within this assembly that need to be replaced in order for everything to work properly once again. Following this, you will then need basic tools such as wrenches and screwdrivers in order gain access to each component individually and make any necessary repairs or replacements before reinstalling your fixture.

Trap Primer

The trap primer is a device that is connected to the plumbing of the bathroom sink. It contains a reservoir, an activation valve and an air gap. The reservoir holds water that is drained from the sink, while the activation valve allows water to enter and flow out of the trap when it is activated. The air gap in this device helps prevent backflow of dirty water into the sink or other plumbing fixtures.

Proper installation of the trap primer will ensure good drainage performance and minimize problems with blocked drains or smell coming from the sink.

Overflow Plate

The Overflow Plate is the small, round metal plate often found near the center of the Bathroom Sink basin. It is usually placed near the tap and may be positioned above or below it. The most common type of bathroom sink overflow plate is a two-part system, consisting of an open rimmed plate and an internal plug. The external rim of the plate typically covers a hole in the sink’s inner wall, while its inner plug seals off an outlet at the back of the sink, forming an overflow channel.

When water collects in a bowl or basin more quickly than it can be drained away, some will find its way through this overflow channel into the plug for release down a pipe beneath. Overflow plates can also:

  • Prevent waste from reaching outlets which have not been properly fitted with a trap.
  • Serve as a barrier which prevents fumes from entering your home through adjoining drains.
  • Prevent objects such as jewellery or toothbrushes from ending up down them by accident.

Sink Strainer

The sink strainer is an important part of the plumbing system for a bathroom sink. It is designed to prevent clogs by catching debris that would otherwise travel down the drain and collect on the walls of your pipes.

The strainer, usually made from metal or plastic, is installed directly over the drain opening and generally consists of a basket or screen which has small holes to block larger objects from entering but still allows water and smaller particles to pass.

The strainer should be regularly checked and cleared of any debris that it has collected to keep the drain flowing freely.


The tailpiece is a plumbing component that connects the drain of your bathroom sink to the plumbing waste system. It runs vertically down from the pop-up assembly, usually through the sink base or, in some cases, behind it and is then connected horizontally to a P-trap underneath.

The tailpiece should be made of plastic or metal and needs to be secured tightly with a slip joint nut and washer upstream of the P-trap. If water continues to run after you have turned off the water supply valve, check and ensure that your tailpiece has been properly secured with no gaps or cracks in between.

Escutcheon Plate

At the back of the bathroom sink is a metal or plastic escutcheon plate. This protective plate serves two main functions. It insulates and covers the pipe where it enters from behind the wall, and it redirects water from the single supply pipe up to the separate hot-and-cold faucet valves.

The underside of this plate should be sealed with a non-hardening silicone caulk to ensure a watertight seal around the pipe. The escutcheon plate also has a threaded collar around its outside perimeter that adjusts via tensioning bolts, anchoring it to the wall and providing support for the drain parts above it.


Although the plumbing of a bathroom sink may seem like a straightforward process, there are many intricacies that go into it. It is important to be familiar with the parts involved and how they fit together in order to properly maintain and repair any issues that may arise.

By understanding each part and understanding the procedures involved, you can ensure that your plumbing system is working efficiently. If any problems arise, you can properly diagnose them in order to resolve them effectively before causing any damage. Keep in mind that most processes you will be able to take on yourself but if something does not look right or is more complex than expected it is always best to seek professional help.

Frequently Asked Questions

What are the main parts of a bathroom sink plumbing system?

The main parts of a bathroom sink plumbing system are the water supply lines, the drain pipes, the shutoff valves, the faucet, and the P-trap.

How do I remove the faucet on my bathroom sink?

To remove the faucet on your bathroom sink, turn off the water supply valves and disconnect the water supply lines from the shutoff valves. Then, unscrew the nut that holds the faucet in place and lift the faucet off the sink.

How do I replace the P-trap in my bathroom sink?

To replace the P-trap in your bathroom sink, turn off the water supply valves and disconnect the drain pipes from the P-trap. Then, unscrew the nut that holds the P-trap in place and lift the P-trap off the sink. Next, install the new P-trap and reconnect the drain pipes and water supply lines.