My Toilet Flush Is Slow: How Can I Fix It?

I finally took notice the other day of our guest bathroom toilet and realized why I hate using it — my toilet flush is slow. Like, slow. And the swirling water that helps waste go down the toilet drain is weak. Let’s talk about what might be happening and how to fix it. But first, you’ll need the basics.

How Does A Toilet Work?

The answer is surprisingly simple — gravity. A toilet is constructed with this premise in mind: water flows downward because of gravity. Let me explain further.

Water is stored in the tank located at the top of your toilet. When you flush it, you’re opening a plug that allows the tank water to flow into the basin (your toilet bowl) below. The water then travels further down into the toilet drain, through what’s called an S trap (that bend in the drain under your toilet), and finally out through your sewer main line.

To sum it up, your flushed toilet water begins at its highest point (your toilet tank), and keeps flowing downhill until it reaches the city’s sewer line to eventually be processed). That’s gravity for ya!

The first flush toilets were used about 2,700 years ago. The versions of what we today would consider a modern toilet was invented by our namesake, Thomas Crapper.

Diagnose And Fix A Slow Flushing Toilet

There are several reasons why your toilet flush is slow. But generally, the problem occurs for one of these three reasons:

  1. clogging issues (by far the most common problem)
  2. part failures (the second most common reason)
  3. water issues (yeah, these can be problems too)

Let’s investigate each of these in more detail.

Clogging Issues That Cause A Slow Flushing Toilet

As stated above, clogs (or blockages) are the number one reason why your toilet flush is slow. The good news is that each of the toilet clogs identified below is fairly easy to identify and fix.

1. Clogged S Trap

The S trap (see the illustrated diagram above) is that S-shaped pipe that is attached just below (and to the left of) the toilet bowl. Because it has this curved shape, waste and debris (but usually too much toilet paper) can easily be trapped and unable to move further. If not dealt with, you will have a no-flush toilet or a slow-flushing toilet.

pink plungerHow do I fix a clogged S trap?
Most of the time, all you need is a common plunger. If the water in the bowl hasn’t already been depleted, you should first remove all but about 2 inches of water. Now, place the plunger over the drain at the bottom of the toilet and pump it up and down very quickly. This should unclog the drain. Just one caution: you can blow out your pipes if you plunge too hard. While you should pump the plunger firmly, don’t overdo it.

If this technique doesn’t work, there are others you can try. Read our article titled “How to Unblock a Drain.”

2. Too Much Toilet Paper or Debris

Using more toilet paper than your system can handle is the most common reason for a clogged toilet. We see it all the time, especially in older homes and toilets. The blockage can occur from a one-time event, but more likely the problem has been building up for a long time.

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Toilet paper is designed to dissolve in water, but it can leave behind a sticky, gummy residue. Some toilet papers are thicker than others (2-ply vs 1-ply). While this might be more comfortable for you, it also is more difficult to flush through your system. This is especially true if your pipes or sewer line already has issues (like cracks, misalignments, corroded interior surfaces that “catch” the debris flowing by, etc.).

How do I fix too much toilet paper in my toilet?
Again, just like the fix for the clogged S trap above, your handy dandy plunger will come to the rescue. Just place the plunger over the drain, and pump the plunger while keeping it sealed to the drain opening. Do this a few times until the problem has been solved. Test by flushing your toilet.

If this doesn’t work, you should try calling your plumber. They will diagnose the issue, and if the problem is due to a toilet paper clog (or other related problems) further down your pipeline, they can root the problem away.

Pro Tip: One of our drain specialists, Ryan Boyce of our Cincinnati and Northern Kentucky location, ran his experiment on toilet papers. Of the big brands, he found that Scott toilet paper dissolved most thoroughly and efficiently. But if you prefer another brand, consider choosing one that comes in 1-ply, which has less paper.

Part Failures That Cause A Slow Flushing Toilet

1. Damaged Fill Valve

The fill valve does what it sounds like; it refills the tank after it has been flushed. Generally, you’ll notice that it’s become a problem because your water continues to run after it has been flushed. This isn’t just annoying. More so, constantly running toilet water is costing you money. Your problem is that the fill valve is probably old and worn out.

Illustration showing the main parts of a toilet tank that can cause slow flushing toilet
This diagram showing the inside of a toilet tank shows the parts — in particular the fill valve and flapper — that cause a slow flushing toilet.

How do I replace a fill valve?
This one isn’t quite as easy as using a plunger. You first need to turn off the water supply to your toilet. Now open the tank and flush; this will remove all of the water from your tank.

Now disconnect the water hose from the fill valve. You do this by unscrewing the nut that connects them (see the diagram above). Remove the valve (pull it up from its base) and replace it with the new fill valve. Reconnect the water hose to the fill valve. Turn back on your water supply and flush. You should be good to go. And we mean that literally. 😉

2. Blocked Jet Holes

This is the reason why my toilet flush is slow. When you flush, fast-moving streams (or jets) of water fill your toilet bowl. These water streams are coming out of tiny jet holes (also called rim holes and inlet holes) located on the underside of the entire rim of your toilet. If not cleaned thoroughly and routinely, over time they’ll clog with hard water minerals (caused usually by using hard water) or bacteria. In either case, you’ll end up with a slow-flushing toilet.

Dirty jet holes and rim holes causing slow flushing toiletHow do I fix blocked jet holes? 
First, look for the jets using a small mirror. Bacterial growth will look like black spots, or maybe dark orange color. Mineral deposits will be scaly and lighter.

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For bacterial growth, you’ll need a bleach solution containing 1 part bleach for every 10 parts of water. Now pour it into your toilet tank’s overflow tube. Wait about 10 minutes and flush. Now clean out the holes using your mirror and a piece of wire. Then clean the underside of your rim with a toilet cleaner. Repeat this process until you have clean jet holes.

For mineral deposits, the process is slightly different. Use vinegar, not bleach. Heat 12 ounces to 120 degrees. Pour into the overflow tube. Wait at least one hour before flushing (the longer you wait, the better). Clean out each jet using your mirror and wire. Flush and repeat the process as needed. When done, clean the underside one final time using a toilet cleaner.

3. Older Toilet

Frankly, you might just have an older toilet with worn-out parts and seals. Some older toilets, even older low-flush toilets, just don’t have the juice you need to get a good flush.

How do I fix an older toilet causing slow flushing?
Your best bet is to simply replace your toilet with a more modern, high-efficiency toilet. Toilet costs generally run between $100 – $500. Standard models will generally be just under 14″ tall (at the seat). And they come in round and oval shapes.

Water Issues That Cause A Slow Flushing Toilet

1. Not Enough Water

This one is pretty easy to diagnose. If your toilet is flushing too slow, remove the tank lid so you can get a good look inside. The water level should be about 1/2 inch below the top of the overflow tube (see diagram above). If not, there is not enough water in the tank to have the flushing power you need. The good news is the fix is easy.

How do I add more water so my toilet flushes faster?
Overhead view of slow flushing toilet tank and overflow tubeJust fill a bucket with water and pour it into the tank (but don’t pour water into the overflow tube) until it is about 1/2 inch below the top of the overflow tube. The overflow tube is a vertical tube with an opening at the top. It has a little rubber pipe that goes into it. In this photo, the overflow tube is white. Once you’ve filled your toilet tank with an adequate amount of water, try a couple of test flushes. The problem should be resolved.

2. Hard Water

As we noted earlier in this article, hard water has a lot of dissolved minerals (like calcium and magnesium). You can easily see hard water after you wash your dishes. It’s that soap scum left behind on your glasses. In a toilet, these minerals build up on the inside of your pipes, making the inside of the pipe smaller and smaller until water flows more slowly.

How do I remove hard water build-up from my toilet pipes?
The do-it-yourself fix is similar to how you cleaned your toilet’s jet holes (see above) but with some differences. Get one quart of white vinegar. Pour quickly into your overflow tube (located inside the toilet tank). Wait overnight: depending on how much build-up you have, it can take a while for the vinegar to loosen and dissolve the calcified minerals.

The next morning, try flushing a few times to see if it has helped. If not, you might need a plumber to remove the build-up for you. On the other hand, you might need to invest in the installation of a water softener, which prevents the build-up of minerals on the inside of pipes in your toilet, water heaters, and other fixtures.

Final Thoughts

In conclusion, there are many reasons behind why your toilet flush is slow. Taking all of these into consideration could help you solve the problem in no time. It might be more of a minor task than you thought it was going to be.

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