Toilet Fills Up Then Drains Slowly: Causes & Solutions

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Considering the number of times we flush the toilet each day, and the kind of material that gets flushed down the drains, you can expect your toilet to experience some kind of problem at some point.

When I was a bachelor living on my own in a new-ish apartment complex, I had a few plumbing problems that were either caused by the previous tenants or my own carelessness (hint: flushing things that shouldn’t be disposed of in the toilet).

At some point in time, one of these problems was my toilet filling up then draining slowly. Of course, the first instinct was to go at it with a plunger. But being a young bachelor with little to no house repair experience, plunging the toilet didn’t always work.

Luckily, I’ve gone a long way from being a clueless bachelor poorly dealing with his own plumbing problems. In this article, I’m going to share with you the tips and tricks on how to fix a toilet that is not flushing properly, particularly a toilet that fills up then drains slowly.

toilet fills up then drains slowly

Why does a toilet fill up then drain slowly

A toilet that fills up normally then drains slowly is an annoying problem to have, especially when you’re trying to flush solids.

Most of the time, the material will not even be completely flushed after the toilet water has gone down. Before we go into how to fix this problem, let’s first find out why this happens.

  • There’s something clogging your toilet. When your toilet isn’t doing things as smoothly as it should, the first thought that you’re going to have is that there’s a clog in the toilet. Oftentimes, this is probably the case. When something is clogging your toilet, the water may go down very slowly after you flush because of the obstruction.
  • A clog can be formed by an accumulation of wet wipes, tampons, sanitary napkins, dental floss, and other toiletries that are better off in a proper trash can. Other times, it can be because of unusual things deliberately or accidentally dropped in the toilet like toys, toothbrushes, razors, and the like.
  • Your toilet ports are clogged. The toilet ports are located underneath the bowl’s rim. Whenever you flush the toilet, the water goes through these ports and into the toilet. Clogs form in the toilet ports because of hard water continuously going through these holes. Over time, hard water creates mineral deposits that harden and accumulate along the ports, causing obstruction and hindering toilet water to flow freely.
  • Low water level in the toilet tank. The water in the toilet tank should always be high enough to give a powerful flush. If you are experiencing a slow draining toilet, take off the lid on the tank behind your toilet. If the water level is more than an inch below the overflow tube, the flush is bound to be weaker. A flush needs to have enough force to create a siphon that will suck the water and material down the drain pipes.

How to Fix a Toilet that Fills Up then Drains Slowly

Calling in a plumber to fix the toilet will probably cost you about $300. Of course, no one wants to spend that amount of money if there’s a possibility of fixing the problem yourself.

With a little bit of effort and some good DIY techniques, here are a few possible fixes to get your toilet flushing back to normal:

1. Get rid of whatever’s clogging your toilet

There are numerous ways on how to get rid of a toilet clog. If your toilet is filling up but draining ever so slowly, something is preventing the water from going down as it should. Fixing a clogged toilet is relatively simple, and it can take just a few household items to work.

Dish soap and hot water 

If you have a wad of toilet paraphernalia clogging up your trap, then it takes a little bit of lubrication in order to push that obstruction into the drain. Using the dish soap and hot water hack is a cheap and easy way to get rid of a clog. 

Simply heat at least a gallon of water and take some regular dish soap into the bathroom. The water should be hot enough but not boiling, as boiling water can crack your porcelain toilet bowl.

Pour one to two cups of dish soap into the toilet, let it sit for about half an hour, then pour the hot water into the toilet just enough so that it doesn’t overflow.

If the trick works, then the water level should start going down faster as the obstruction is being pushed further down the drain and into the sewage.

Use a plunger

A cheap plunger may not work as effectively as one with a flange that narrows at the end. This type of plunger gives a better suction and can pull the clog up more easily.

To get rid of a clog using the plunger, simply seal it over the mouth of the toilet, then push up and down in order to create a suction. After a few minutes, the clog should be dislodged.

plunger for overflowing toilet
Bring the clog up using a toilet auger

A toilet auger, otherwise known as a toilet snake or closet auger, is a tool that is maneuvered inside the toilet in order to pull up the clog.

For a list of the best toilet augers, click here.

Toilet augers can cost about $50, but if you want to save more money, you can unravel a wire coat hanger and use it as a makeshift hook to bring out the clog. Just remember to use gloves!

Use commercial toilet cleaners and dissolvers

Using toilet cleaners or organic solvents is not always recommendable, since these chemicals can be quite harmful to the environment.

However, if none of the other fixes work for you, it may be time to try dissolving the clog instead by pouring an entire bottle of solvent in the toilet.

2. Clean out the toilet ports

Cleaning out the toilet ports is very easy. All you have to do is scrape around the holes in order to get rid of the hard material that’s clogging them. You can do this by using a screwdriver, a wire coat hanger, or any other metal tool that you can use.

On the other hand, you can also pour a cleaning solvent in the overflow tube to get rid of bacteria or mineral deposits.

  • For bacteria, use one part bleach and ten parts water.
  • For mineral deposits, use 8 to 12 ounces of heated vinegar.

Let these liquids go down the overflow tube and through the toilet ports. Leave it to sit for about half an hour before flushing.

3. Adjust the water level in the toilet tank

If you see that the water level in the tank is not high enough (e.g. an inch or half an inch below the overflow tube), adjust it by manipulating the float. 

If the float is at the end of a metal rod, raise the rod until the water is high enough.


On the other hand, if your toilet has the type of float that can slide up and down the rod, pinch the clip that attaches the float to the rod and slide it up.

The water level should be at least half an inch or an inch below the overflow tube.