Understanding the plumbing of the bathroom sink

Some plumbing components names are difficult to understand. It will make it easier to find the correct names for parts if you need them. For example, the bathroom sink has many basic components that can be damaged, leaking, or blocked. These parts are easily replaceable and readily available. When shopping for parts, you must be aware of what to look for.

Shutoff Valves

Shutoff valves are small metal valves that are located between the incoming water supply lines and the supply tubes or hoses that connect to the tailpieces of the sink faucet. The handle of most shutoff valves is oval-shaped and football-shaped. This allows you to open or close it. Shutoff valves are also known as stop valves. They allow you to shut off water at the sink and not the entire house. You can see them in pairs. One valve controls hot water, the other cold water. Many shutoff valves are made of compression fittings, which means they can be attached to water pipes without the need to solder. However, you will need to shut off the water supply to the house in order to replace the shutoff valve.

Supply Tubes

You will often see two narrow supply tubes running from the shutoff valves to the tailpieces of the sink faucet. You can choose to make them from braided wire mesh or plastic mesh (usually white), chromed copper, solid plastic (often grey), or even solid plastic. These are typically connected to tailpieces or shutoff valves using attached nuts. Sometimes, these supply tubes fail and you may need to replace them.

Tailpiece Drain

The sink tailpiece is the straight section that connects to the sink drain fitting. The tailpiece connects to the port at the back of the sink if it has a pop up drain. The tailpiece is usually attached to the drain fitting using a slip nuts–a threaded rings that can be tightened or loosened manually (or with gentle pressure from channel-typepliers). A tapered plastic washer is located underneath the nut to create a watertight seal.


Double-purpose slip-nut joints can be very useful because if an item is ever dropped into the sink drain you can easily disassemble the slipnut joint to retrieve it.


The U-bend (3a), and the trap arm (3b) are the two main parts of the P-trap. These two sections of pipe bend to allow your sink to be connected to the sewer line. The curved trap, which holds water and prevents sewer gases from rising out of your sink drain, is a simple safety device. To prevent gasses from passing through, the bottom of the U bend is kept filled with water. Every time you flush water down the drain, any old water is removed and replaced with fresh water. Although the P-traps are made with slip-nut joints in most cases, you might find solvent-glued traps in older homes. It’s a good idea if you have one of these to replace it with a slip-nut joint.

Drain Pipe

The household plumbing system is connected to the sink drain pipe. The trap arm is connected to it with a slip-nut joint. Slip nuts make it easy to repair sink plumbing. The majority of bathroom sink drainpipes are 1 1/2 inches in diameter. However, they can be larger or smaller.