Why Is My Drain Slow (and How Do I Fix It)?

Most slow drains are a buildup of hair, soap scum, or grease within a foot or two of the drain opening, which you can usually clear with a plunger, a plastic zip tool, or a hand snake. If several drains are slow at once or the lowest drains in the house back up, the clog is likely in the main line and needs a plumber.

How to tell where the clog is

Before you reach for any tool, figure out how big the problem is. Run water in a few fixtures around the house and watch.

• Only one drain is slow. The clog is almost certainly close to that drain: the stopper, the P-trap, or the short pipe right after it. This is a DIY job most of the time.

• Two drains in the same room are slow. The clog may be in the branch pipe they share. A hand snake can often reach it.

• Drains all over the house are slow. The problem is in the main line or a shared vent. Stop using water as much as you can and call a plumber, because the next step is usually sewage backing up.

• The lowest drain backs up when you use another fixture. For example, water coming up in a basement floor drain or first-floor shower when the washer drains or a toilet flushes. That is a classic main line clog.

• You hear gurgling but nothing seems clogged. The drain may not be getting enough air. Plumbing vents can be blocked by leaves, nests, or ice, which slows drainage and can let sewer gas into the house.

How to clear a slow drain yourself

Start with the least invasive option and work up. Most single-drain clogs are cleared by step one or two.

1. Clean the stopper. Pull out the pop-up stopper or unscrew the tub or shower strainer and clean off the hair and gunk. On a bathroom sink, the stopper is usually held by a horizontal rod behind the drain pipe under the sink.
2. Use a zip tool. A thin plastic strip with barbs, about $3-$10. Push it down the drain, pull it back, and it brings the hair with it. This clears a large share of bathroom clogs.
3. Plunge it. Use a cup plunger for sinks and tubs. Cover the overflow hole with a wet rag so the pressure goes down the drain, and make sure there is enough water to cover the plunger cup.
4. Clean the P-trap. Put a bucket under the curved pipe below the sink, loosen the two slip nuts by hand, and empty and rinse the trap. Reassemble and hand tighten.
5. Use a hand snake. A 15 to 25 foot drain auger reaches past the trap. Feed it in until you feel resistance, crank it to grab or break up the clog, then pull it back slowly and flush with hot water.

When it is the main line

A main line clog needs a plumber or drain service with a long, powered auger. If the same main line clog keeps coming back, ask about a camera inspection. A small camera fed into the line shows whether the problem is roots, a sag where waste collects, a collapsed section, or just buildup.

Hydro jetting uses high-pressure water to scour the inside of the pipe and is often used for grease and root buildup. It is more thorough than snaking but costs more, and it is not right for every pipe, which is another reason a camera inspection first is worth it.

If your home has a septic system, slow drains throughout the house can also mean the tank is full or the drain field is struggling. That is a call for a septic service rather than a plumber.

How to keep drains clear

• Use a hair catcher in tubs and showers. They cost a few dollars and prevent most bathroom clogs.
• Keep grease, coffee grounds, and fibrous food scraps out of the kitchen sink. If you have a garbage disposal, run plenty of cold water while it works and for a few seconds after.
• Pull and clean bathroom sink stoppers every few months.
• Flush only toilet paper. "Flushable" wipes are a common cause of main line clogs.