How a Shower Drain Works: Plumbing Diagram

Shower drains are an integral part of our home plumbing system that we take for granted. We turn the water on, enjoy the soothing hot water after a long day of work, and expect the water to simply wash away to the main drain line and out into the sewer—without any sewer gases filtering into our home.

Several essential shower drain components make this happen. Below, we’ll look at a shower drain plumbing diagram to understand how these various parts work together and discuss what to do if your drain isn’t working properly.

What Are the Parts of a Shower Drain, and How Do They Work?

Your shower drain is a complex network of pipes with various components, but we can really boil it down to five core parts that the average homeowner should know about.

Strainer

The strainer is the only part of the shower drain that you should be able to see in your daily life. It’s the cover over the top of the hole in the shower floor that leads into the actual drainage system, and it’s designed as a barrier to keep soap scum, hair, sock fuzz, and other debris from entering the drain.

You may also hear this part referred to as a drain cover. While your drain can technically function without a strainer, you’ll have to deal with a lot more debris getting into your drainage system—and, thus, more frequent clogs.

Riser

The riser is the vertical pipe directly beneath the strainer. Water that drains from the shower goes down this pipe and through the P-trap (see next section) before filtering out through the main drain line that carries wastewater out of your home.

P-Trap

The shower P-trap is an essential component of your shower’s drain system. Without it, sewer gases would filter in from the main sewer line, meaning noxious fumes from everybody’s waste would enter your home. That’s why every plumbing fixture, from toilets to showers to sinks, includes some kind of trap.

How do P-traps work? Water sits in the bend of this U-shaped pipe, creating a seal that prevents gasses from passing through. (The pipe also looks like a P that has been turned on its side.)

When you run the shower and water filters down the riser, it pushes the water sitting in the trap outward toward the drain line. However, when you shut the water off in the shower, a new collection of water gets “trapped” in the P-trap, maintaining a barrier to prevent gases from flowing through.

Because of this shape, P-traps can commonly become clogged. There are several ways to unclog a tub drain, including using a trusty plunger or, for a more effective solution, by unclogging the shower drain with a drain snake or auger.

While over-the-counter cleaners are rough on your pipes, we do have a few homemade drain cleaners that are safe to use, which we recommend in a pinch.

Want to get rid of a clog in your shower’s P drain? Read our guide on how to unclog a bathtub in six easy steps.

Similarly, your P-trap can dry out; that is, there are scenarios in which water won’t get trapped inside the bend, and noxious sewer gases can enter your home. It’s important to run water down the drain regularly to prevent this. If you have a guest shower that doesn’t get used often, for instance, it’s still important to run the water once a week or every few weeks for a few seconds just to refresh the P-trap.

P-traps can also dry out faster in dry climates or during the winter when the heater is run more often. They may also dry out if there are issues with the vent stack.

Vent Stack

Any plumbing fixture with a trap, including a shower, needs a plumbing vent. A vertical pipe connected to the horizontal drainage pipe will travel upward toward the roof of your home to vent.

Air moves down this vent stack as waste moves through the drain line. This allows the water to move more smoothly through the plumbing system as it drains. Without this assist from the vent, the water may flow more slowly (or even result in standing water in your tub). If there are issues with the vent stack, you may also hear gurgling sounds when the water drains and fumes from the sewer pass through your drain (if the plumbing vent is dried out).

Drain Line

The drain line is the ultimate destination for your wastewater. After it successfully descends the riser and passes through the P-trap, water will travel to your home’s main drain line and out to the sewer.

What Are Common Shower Drain Problems? 

The main shower drain problems that you’ll likely run into are slow drainage and bad smells. A slow shower drain can lead to standing water that creates a ring of soap scum and debris around the bottom of the shower. The larger issue, however, is that the clog causing slow drainage is made of organic material that will smell worse and worse as the material breaks down.

How to Maintain the Different Parts of a Shower Drain

Maintaining your shower drain is easy, especially if you regularly use the shower. Routinely allowing hot water to flow down the drain should replenish the water in the P-trap, and using a drain cover over the strainer can prevent hair and other debris from getting caught in the trap.

If you don’t use the shower regularly, pour hot water down the drain once a week or every few weeks. You can also pour vinegar and baking soda down the drain to unclog the shower and remove foul odors.

Here are a few more tips to keep your drain clear and keep bad smells at bay:

• Use a hair removal tool to pull hair out of the drain.

• Put a few drops of essential oils in the drain before using the vinegar and baking soda.

• Remove hair from the drain cover after each shower.

• Use a drain snake periodically to remove stubborn clogs or debris.  

• Unclog a shower with standing water with a plunger. 

Cost to DIY Shower Drain Part Repair vs. Hiring a Pro

Unclogging a shower drain is an easy enough DIY project. You’ll just need to spend $20 to $40 on a drain snake or auger—or even less if you make a homemade cleaning solution. Sometimes, a simple plunger is enough to unclog a drain (though we recommend having a separate plunger from the toilet plunger).

If there are larger issues, like with your home’s main drainpipe, the vent stack, or a leaky trap, we highly recommend calling a shower installer near you to assess the problem and make the changes. How much it will cost depends on the source and severity of the problem. On average, plumbers cost between $45 and $200 per hour. There’s usually a service fee just for showing up to assess the problem.