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How to Fix a Slow Draining Tub

A slow-draining tub is a common problem, and an irritating one, too. Nobody wants to stand in a deepening pool of murky water while taking a shower. Read our guide to fixing a clogged tub.

Plunger used to unclog a sink drain. iStock

There are several possible causes for a slow-draining shower. Let’s address the most common cause first: a clog at the shower drain, or in the P-trap just below it.

You don’t have to call in a plumber to investigate and fix this issue, and the only special tool you need is some sort of plumber’s snake, which you can buy at any hardware store or home center.

Professional-grade plumbing snakes can cost hundreds of dollars, but you can buy one powered by a drill or by hand for $25 or less. A hand-powered snake may also be called a drum auger if you are doing a product search. A plumber’s snake–even an inexpensive one—is a good tool to have. It can enable you to clear clogs in toilets, sinks, and shower units.

Tub Drain Anatomy

Before you get started, it’s smart to familiarize yourself with the anatomy of a typical tub. The tub’s drainage system consists of an L-shaped assembly that includes the tub drain, the overflow tube, and a stopper mechanism that is raised and lowered inside the overflow tube.

The tub’s drainage assembly feeds wastewater to a P-trap, which can also be a clog location. Even if your tub doesn’t have a slow draining problem, it’s good practice to clean out the tub drain once a year or so. This proactive strategy will prevent soap scum and hair from accumulating.

Snake the Drain to Clear Clogs

To begin, remove the tub’s drain cover or drain plug. Depending on the configuration of your drain, you’ll need a screwdriver and/or a pair of pliers to do this.

  1. Cover the exposed drain with a towel. This will prevent a dropped tool from marring your tub, while also preventing loose screws from falling into the drain.
  2. Next, unscrew the cover plate for the tub’s overflow tube, which also includes the stopper mechanism. (Hold onto the cover plate screws; many have been lost down an open tub drain.) Carefully withdraw the stopper linkage up and out of the overflow tube.
  3. These two disassembly steps will probably reveal a tangle of hair and soap scum. There’s more to come. To get at it, insert the tip of your snake into the tub drain and push through the drain line, twisting the snake as you go. The snake won’t go very far; you’ll hit the overflow tube pretty quickly.
  4. Pull the snake free and remove the messy stuff you’ve snagged. Then work the snake down the overflow tube the same way, twisting as you push. Here your goal is to make the snake travel farther, past the tub drain, and into the P-trap, where there’s probably more debris to clear.
  5. After pulling the snake free and removing the goop, pour some water down the tub drain and see if you’ve cleared the clog. If the water drains quickly as it should, you can put everything back together and call it a job well done.
  6. If your snaking session yields plenty of hair and soap scum, but still leaves you with a slow drain, there’s a good chance that the P-trap is still obstructed. To clear it, plug the overflow hole with a rag and fill the tub drain with hot water, which will help to soften and loosen soap scum.
  7. Then vigorously pressurize the drain line, use a plumber’s plunger.

Clearing a Clogged Vent Pipe

If a tub continues to drain slowly even after the basic cleaning described above, the problem might be caused by a clogged vent pipe.

Vent pipes extend through the roof and are open to the atmosphere, equalizing pressure in drain lines so that a vacuum effect won’t disrupt drainage. Because a vent pipe is open at the top, it can be clogged by sticks, leaves, and other debris. Blockages can also occur because of insects or animals.

If you suspect that a clogged vent is causing household plumbing to drain slowly, you can investigate just like a plumber would:

  1. Get up on the roof, shine a light down the vent, and see if you can spot an obstruction. If one exists, do your best to pull the debris up and out with your snake.
  2. Then put the end of a garden hose down the vent and have someone turn on the water for several seconds.
  3. Listen as the vent fills up with water, then listen again after the water is turned off. A telltale whoosh will let you know that the obstruction has been pushed down the drain.