Beginner’s Guide to Identifying Common Plumbing Parts (So You Can Order the Right Replacement)

Why it helps to know the names of your plumbing parts

If you’ve ever stood in the plumbing aisle staring at a wall of parts thinking, “Is this even the right thing?” you’re not alone. The problem usually isn’t that the repair is too hard—it’s that the part names and shapes are confusing.

This guide walks through the most common plumbing parts in a typical home so you can identify what you’re looking at, describe it clearly, and order the right replacement the first time.

Big picture: three places you’ll see most plumbing parts

Most of the everyday plumbing parts a homeowner touches fall into three zones:

1. Faucets — cartridges, stems, aerators, O-rings.
2. Under-sink drains — P-traps, tailpieces, slip-joint nuts, washers.
3. Toilets — fill valves, flappers, supply lines, shut-off valves.

Once you know what each of these pieces is called, it becomes much easier to search for the right part online or ask for help in a store.

Faucet parts: what you see above and below the sink

1. Faucet cartridge or stem

Inside most modern faucets is a cartridge (single-handle) or a valve stem (often in two-handle faucets). This is the part that controls water flow and temperature. When it wears out, you usually get:

• A drip from the spout that doesn’t stop, even when the handle is “off.”
• Difficulty getting the right temperature.
• Stiff or jerky handle movement.

Cartridges and stems are brand- and model-specific. When you remove one, take clear photos next to a ruler and note the faucet brand to help match it.

2. Faucet aerator

The aerator is the small fitting that screws onto the tip of the faucet spout. It mixes air into the water to control flow and reduce splashing. Symptoms of a problem aerator:

• Water spraying sideways or in strange directions.
• Very weak flow even though other fixtures have good pressure.

Aerators are usually easy to replace. When you remove it, note:

• Whether it’s a male or female thread (threads on the outside vs inside).
• The diameter (common sizes are 15/16" and 55/64").
• Whether the faucet uses a hidden or “cache” aerator that needs a special key.

3. Faucet supply lines

Under the sink, you’ll see flexible supply lines running from the shut-off valves to the faucet. They can be braided stainless steel or flexible plastic.

When replacing supply lines, pay attention to:

• Length (measure the existing line end-to-end).
• Connection size at the valve (often 3/8" compression).
• Connection type at the faucet (varies by brand/model).

Under-sink drain parts: the stuff below the basin

1. P-trap

The P-trap is the curved section of pipe under your sink. It holds a small amount of water to block sewer gas from coming back up the drain.

Common reasons to replace a P-trap:

• Leaks at the joints or cracks in the plastic/metal.
• Heavy buildup that’s difficult to clear.

When shopping for a replacement, note:

• Material (PVC, ABS, or metal such as chrome-plated brass).
• Size (1-1/4" is common for bathroom sinks, 1-1/2" for kitchen sinks).
• Whether you need a full trap kit (including nuts and washers).

2. Tailpiece and extension

The vertical pipe that comes down from the sink drain to the P-trap is the tailpiece. Sometimes an additional extension tube connects the tailpiece to the trap.

If you see leaks or corrosion in this area, note:

• The diameter (match the P-trap size).
• The approximate length you need to reach from the sink to the trap.
• Whether your current pieces are slip-joint (held with nuts and washers).

3. Slip-joint nuts and washers

The connections on a typical under-sink drain are held together by slip-joint nuts and tapered washers. Over time, these washers can harden or deform and start to leak.

If you’re chasing a small drip:

• Look closely where pipes join. The plastic or metal nut and the tapered washer behind it are often the issue.
• Washing-machine-style overtightening can actually make leaks worse. Snug plus a small extra quarter-turn is usually enough.

Toilet parts: inside and around the tank

1. Fill valve and float

The fill valve refills the tank after each flush. It works with a float that rides up and down as the water level changes. When this setup fails, you get:

• A toilet that keeps running or hissing.
• Water spilling into the overflow tube.
• Very slow refills.

Modern replacement fill valves are often “universal” but you still want to note:

• Whether your toilet is a standard height or a low-profile model.
• Where the water supply enters the tank (bottom vs side).

2. Flapper

The flapper is the rubber or silicone piece at the bottom of the tank that lifts when you flush and seals afterward. A worn flapper is one of the most common reasons for a running toilet.

Before buying a new flapper, note:

• Whether your toilet uses a 2" or 3" flush valve opening.
• How the flapper attaches (ears on the overflow tube vs a ring style).
• The brand of the toilet if you can find it (some models are picky).

3. Toilet supply line and shut-off valve

The supply line runs from the wall or floor shut-off valve to the bottom of the toilet tank. The shut-off valve (also called an angle stop) is what you turn to kill water to the toilet when you’re doing repairs.

If you see corrosion, rust, or evidence of past leaks:

• Measure the length of the existing supply line.
• Note the connection type at the toilet (most modern toilets use a standard 7/8" ballcock connection).
• Consider upgrading to a new shut-off valve if the old one is hard to turn or doesn’t fully shut off water.

How to document parts before you shop

Whether you’re dealing with a faucet, sink drain, or toilet, a few simple habits make matching parts much easier:

• Take clear photos from multiple angles before you disassemble anything.
• Use a ruler or tape measure in at least one photo so size is obvious.
• Write down brand names and model numbers if you can find them.
• Keep small parts in a labeled bag so you don’t lose screws or clips.

Putting it into practice

The next time you find a leak or a running toilet, pause before you head to the hardware aisle. Spend a few extra minutes to:

1. Identify which zone you’re working in (faucet, under-sink drain, or toilet).
2. Use this guide to name the specific part you’re looking at.
3. Gather measurements, brand info, and photos.

Armed with the right names and details, you’ll be able to order parts with confidence, compare options more easily, and avoid repeat trips back to the store because something “almost fit” but not quite.