Shower not clogged but won’t drain? try these tips7 min read

When a shower doesn’t drain correctly, many homeowners persist in attempting to unclog it, but it’s ineffective. Often the issue is not immediately visible and can be found in a different part of the house entirely. 

A shower draining poorly that isn’t clogged may result from P-Trap problems, a broken tub lever, a blocked vent, old pipes, or tree roots. P-Trap and tub lever issues affect only the shower, while a blocked vent, outdated pipes, and tree roots may affect multiple fixtures. 

As someone who grew up in a Victorian house with never-ending plumbing issues, I’ve encountered this issue myself. I’ve researched and tested the most common causes of the shower not draining correctly, despite being clear of blockages. 

Why Is Your Shower Draining So Slowly?

Showers can drain slowly without the drain being clogged for the following reasons: 

  • P-Trap Issues
  • Broken tub-lever 
  • A blocked vent
  • Old and insufficient pipework
  • Tree roots 
Signs to look out forPossible Cause
Only the shower is affected. Gurgling, foul smells and the shower is slow to drain.The P-Trap is clogged or installed incorrectly.
Only the shower is affected and you have a tub-shower combo. No gurgling or smells.The tub-lever may have malfunctioned.
The shower in addition to close by plumbing fixtures are slow to drain. The toilet may bubble and the shower gurgles.A blocked vent.
The plumbing work is old and struggles to drain whilst multiple appliances are being used.Outdated pipework.
There are trees close to your house and other plumbing fixtures are also slow to drain.Tree roots have grown into the drainage system.

I’ll walk you through each of these reasons in detail. I’ll talk you through the signs to look out for as well as how you can solve your slow-draining shower. 

Shower Troubles: Investigating Vent Clogs 

Shower drains need vents to work properly and when a vent gets clogged, it can cause your shower to drain much slower than it should ordinarily. This can often be the case even where the drain itself is not clogged. 

For those who don’t know, a vent is a necessary plumbing fixture (required by plumbing codes in many states) and allows air from your waste pipes to escape. This equalizes pressure in your waste pipes allowing for a normal flow of wastewater. 

You’ll often notice vent stacks on the top of buildings and I have shown a photo just below. Vents typically get bogged up by things like debris (leaves, twigs, dirt), animal nests, or by ice and snow.  

Plumbing vent
This is what a plumbing vent looks like on the top of a house.

In addition to your shower not draining, you may also notice the following things: 

  • Water takes a long time to drain from the shower, in addition to other sinks within the home
  • Gurgling sounds as water drains from the shower
  • The sink omits a foul smell
  • Water backs up into other sinks. For example, maybe your bathroom sink fills up with water as your shower is trying to drain
  • Bubbling toilets when flushed

You’ll most likely only have a blocked vent where you are noticing other plumbing fixtures within the home are slow to drain. For example, if your bathroom sink is also slow to drain that could suggest that your shower and sink are sharing a blocked vent. 

How to fix a blocked vent 

The best way to clear a plumbing vent is by getting on your roof. If your roof is dangerous or steep it’s best to get a professional in. 

Hold your hand over the vent stack whilst an assistant flushes a toilet. If you don’t feel suction that’s another good indicator that the vent pipe is blocked. 

From there, you have two options: 

  1. Use a plumbers snake (on Amazon). A plumber snake is a long coiled device that can stretch as far as 50 feet. Insert the coiled end into the vent pipe and thread it down by rotating the handle clockwise. Apply some pressure to unblock anything you might find. 
  2. Use a garden hose. If your hose stretches far enough to the roof, you can give the vent a blast of water for around 5 minutes. 

If you can’t access the vent from the roof another option you have is clearing the vent from the attic. All vents will lead to a large drain called the main stack. 

  1. Use a hacksaw to cut a small section out of the vent – it only needs to be big enough to thread a plumbing snake into it. 
  2. Insert the snake and guide it downward until you feel it pushing against the clog. Crank the handle and keep turning it to cut through the blockage. 
  3. After removing the clog you’ll need to repair the hole you made in the PVC pipe. Use PVC coupling (on Amazon) to join the cut ends of the vent pipe securely. 

P-Trap Problems: A Common Plumbing Headache

The P-trap is a pipe that sits underneath plumbing fixtures and its job is to prevent sewer smells from entering your home. If the nearby vent is blocked, the P-trap is clogged, or the P-trap is not installed correctly, it can prevent your shower from draining even when the shower drainage is not clogged.

P-Trap in shower

A clogged P-trap can obstruct your shower drain. Even when homeowners clear the top of the drain, a blocked P-trap can still impede proper drainage. 

Clearing a P-Trap is more challenging compared to blockages closer to the shower basin and this can lead homeowners to doubt whether the slow drainage of your shower is due to a clog. 

Other signs of a blocked P-Trap include gurgling sounds, foul odors, and water backup. The best way of clearing a P-Trap clog is by using a plunger. 

The method I normally use with plungers (which is really effective) is to first pour hot water down the drain, and then plunger the drain. Make sure you have a good seal and move the plunger up and down a couple of times.

Plungers are preferable because the pressure can sometimes free up a stuck stopper mechanism, which is another issue some showers face. If this doesn’t work you may need to actually remove the P-Trap and clear it manually. 

Lastly, if the P-Trap has been installed incorrectly, this could cause your shower to drain poorly. This is normally the case where the drainage pipe does not slope down sufficiently to draw water at the required volume.

The symptoms of this are similar to a blocked P-Trap. If you suspect this to be the case, I’d recommend reading the rest of the article to make sure before contacting a plumber to reinstall the P-Trap. 

The Tub Lever In Tub-Shower Combos

A bathtub trip lever is a small lever usually located on the overflow drain cover, and when you lift it, it operates a mechanism that opens or closes the bathtub drain, allowing water to either stay in the tub or drain out. 

When a trip lever malfunctions it can either cause water to drain too quickly from the bathtub or not at all. 

Once you’ve ensured your tub is not clogged, inspect your drain lever. Sometimes levers won’t stay in a downward position when they malfunction and in order for your tub to drain, it needs to be held down. 

If this is the case I’d recommend replacing your tub lever. The good news is that drain kits (on Amazon) are very cheap and this job only takes around 5 minutes.

  1. Check for clogs and gather the replacement kit. 
  2. Remove the old parts. You’ll need to locate the pin that holds the weight to the old lever and remove it. If you notice any ruse, that’s probably why your lever isn’t working properly. 
  3. Install the new parts. Attach the new pin from your kit to where you removed the old one. Put the weight unit back on the drain piece, making sure the new latch cover faces downwards. Let the weight unit fall into position and reattach the screws. 

Here’s a great instructional video showing you how to replace your tub lever: 

Vintage Pipes: Masters of Slow Drainage  

Outdated plumbing fixtures can lead to a host of problems, and this is often the case in older houses. 

Sewer lines experience significant wear and tear. Pipes found in older homes were normally constructed prior to the widespread use of modern appliances like garbage disposals, dishwashers, and pressurized power showers. As a result, they are more prone to failure, particularly when extensive remodeling has occurred. 

In a typical household, a main drainage pipe collects wastewater from fixtures and appliances (sinks, toilets, showers, washing machines, etc.), carrying it out to the sewer or septic system. While modern main drainage pipes are typically 4 inches in diameter, some older homes may still have 1-inch drain pipes.

With an insufficient main drainage pipe, you’ll notice slow drainage in the shower, especially where other appliances are being used, like the dishwasher. This can also result in standing water in the shower. You may also notice backups in other plumbing fixtures as well as more frequent drain blockages. 

Secondly, old homes sometimes develop ‘pipe bellies’ which is where pipes shift creating negative slopes. These bellies can hold water, promote clogs, and attract tree roots. This can lead to frequent clogging as well as a slow-draining shower when it’s not clogged. 

If you suspect either of these situations, you should consult a plumber and consider plumbing upgrades. You may need to replace the undersized main drainage pipe or reconfigure the plumbing system. 

Tree roots disrupting your drainage

Tree roots can pose several problems for plumbing drainage systems. Tree roots are naturally attracted to the moisture and nutrients in sewage pipes. They can infiltrate small cracks or joints in the pipes and grow inside, causing blockages. This leads to slow drainage and backups.

Massive Tree
Tree roots grow around 2 – 3 times the radius of the canopy. This is a picture of me next to a Redwood. Hopefully, you don’t have Redwoods growing into your plumbing!

Even if roots don’t completely block the pipe, their presence can constrict the flow of wastewater, reducing the system’s efficiency and potentially causing overflows.

If you live in close proximity to trees, or you have older sewer pipes made of clay or concrete, unfortunately, you may be more susceptible to tree root damage. 

Are there other drains further down the drainpipe from your shower? If they are also slow, and you hear gurgling noises from these drains whilst showering, it’s possible a sewer pipe going out from your house has tree root damage. 

If this is the case you’ll need to get your sewer lines replaced and unfortunately it’s not cheap. It’s likely to cost you around $500 for the tree root removal and a further $50 – $200 per foot to replace damaged pipes. 

How Does a Shower Drainage System Work?

Shower drains are an essential part of every shower, and they play a crucial role in ensuring that water flows away from the shower area efficiently. 

Understanding how a shower drain works can help you maintain and troubleshoot any problems that may arise.

Drain Cover

The drain cover is the visible part of the shower drain on the floor. It is designed to prevent debris from entering the drain and provide a smooth surface for water flow. The drain cover can be removed for cleaning or maintenance purposes.

Strainer

The strainer sits just beneath the drain cover and catches any debris that may enter the drain. Therefore, it is essential to clean the strainer regularly to prevent clogs and slow-draining water.

Trap

The trap is a curved section of pipe that sits below the drain and is designed to hold water to prevent sewer gases from entering the shower area. 

The trap is also a common location for debris to accumulate, so it is important to clean it regularly to prevent clogs.

Waste Pipe

The waste pipe is the section of the plumbing system that carries water away from the shower drain and into the sewer or septic system. The waste pipe is typically made of PVC or ABS plastic and is connected to the trap using compression fittings.

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Hi, I'm Ed, and I run BuildFanatic! I enjoy providing the best possible information on a range of home improvement topics.

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