Toilet Fills Up With Water Then Drains Slowly? (Fix It Now!)

Nick Durante
by Nick Durante

Nothing is more frustrating than toilet and plumbing problems, especially when you don’t know the cause. Toilet flush power can vary, but you should always be able to count on your toilet draining properly. That’s not always the case, however, so why is your toilet filling up with water and draining slowly?

Toilets fill up with water and drain slowly if there is a blockage deep in the drain. Low water levels in the tank due to a damaged fill valve also cause the water to drain slowly. Mineral buildups and clogged siphon jets and rim holes make it harder for your toilet to drain water as well.

Removing blockages is as easy as snaking the drain, but other problems, like mineral hard water, are trickier. Let’s take a look at what you should do when your toilet fills up with water and then drains slowly.

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Possible Causes

You can diagnose the cause of your slow-draining toilet by inspecting the bowl and tank. Common causes for slow draining toilets include blockages, mineral buildups, damaged fill valves, and a low water tank. Follow along as we explore each reason why your toilet may drain slowly and what you can do to fix it.

1. Blockage

Toilets often drain slowly when there is a blockage within the pipes. Blocked drains are the most common problem homeowners experience with their toilets. Not all blockages are severe enough to clog the toilet, so they can be less obvious at first.

Your first instinct is to unclog the toilet if it won’t flush, but that is also the solution when it drains slowly. Toilets can slowly lose water due to blockages if it causes a leak, or it can cause the water to rise and slowly drain. Some blockages occur deep within the drain, and that causes the slow action after flushes.

Luckily, you can solve this problem by removing or dissolving the blockage.


Use a drain snake to remove a blockage in the toilet. Drain snakes are the best option for this because toilets that drain slowly often have deep blockages that are hard to reach. You can reach far down the drain with a snake, and it can break up the blockage.

You can plunge the toilet if the blockage is not too far down the drain. Insert the plunger into the toilet above the hole and pump it up to 10 times. The suction will knock blockages loose and improve your toilet’s draining quality.

Solutions like baking soda and vinegar also work to dissolve the blockage. You can use bleach, but you need to dilute it with water, so you don’t damage the pipes. Be careful above chemicals, because it’s dangerous to leave Drano or Liquid Plumber in the drain for too long.

2. Water Tank Is Low

Your water tank can run low if there is a problem with any of the floats or valves. Toilet tanks run low when the float ball drops too low. This causes the water to lower in your tank, and ultimately in the toilet bowl itself.

Low water in the tank can cause your toilet to drain slowly even if it fills up with water. The tank is one of the components that are responsible for flushing power. Your toilet cannot flush and drain properly if there isn’t enough water in the tank.

Fill tubes and fill valves can also fail and negatively affect your toilet’s draining capability. All of these components can be adjusted, repaired, and replaced as needed.


Take the lid off of your toilet tank so that you can increase its water content. Look down at the float ball in the tank and its adjacent fill valve. Carefully grab the rod next to the float ball and fill the valve to adjust the water level.

Use your fingers to turn the rod’s screw in a clockwise motion. Watch the float ball raise as you turn the screw, and the water level will rise. Stop turning the screw once the water reaches the level that it normally is at.

Place the lid back on the tank and wash your hands. Now, flush the toilet several times to see if it drains properly as the water fills the bowl. If that didn’t help, you’ll need to troubleshoot your toilet with the other options in this guide.

3. Mineral Buildup

Minerals can build up inside of the toilet bowl and the tank as well. You can find calcium and magnesium in your home’s water supply and it builds up over time. The minerals continue to become denser and more visible the longer that you let them go untreated.

This is referred to as “hard water”, and it is visually unappealing. It makes the toilet look dirtier than it even is, and it affects how the toilet drains. Minerals don’t necessarily damage the pipes, but they do make it harder for the water to drain.

The minerals clump up if you don’t treat them, and it can partially block the drain. These clumps get big enough that water cannot easily pass through them. Your toilet will drain more efficiently if you treat it for minerals, and it doesn’t take long.


Remove the mineral buildups from your toilet with an enzyme, such as Calcium, Lyme, and Rust Remover. Any acidic toilet bowl cleaning product can help to break down and remove clumps of minerals in your toilet. Make sure to put on gloves as these chemicals can hurt you or damage your skin with prolonged exposure.

Pour one cup of Calcium, Lyme, and Rust Removal into your towel bowl. Allow the chemical to sit in the water and start a timer for two minutes. Carefully and thoroughly scrub the toilet with a toilet brush, including the drain hole, for a few minutes.

Exercise caution when you use the toilet brush on the drain hole, so it doesn’t become lodged. Flush the toilet several times to wash the chemicals down the drain, and your toilet should drain quickly. You can repeat this process several times until the results take.


The easiest way to prevent mineral buildups in your toilet is to lower the water temperature. Turn down the temperature at your water boiler to help minimize minerals in your water. Otherwise, you can occasionally add apple cider vinegar to our toilet water, let it sit, and flush it.

The acidity of the apple cider vinegar helps fight and prevent minerals from clumping up. Standard vinegar works as well and helps break up clumps of minerals and lower the mineral content in the water. Otherwise, you can invest in a water softener to filter minerals out of your water supply and toilet.

4. Damaged Fill Valve

Fill valves can become damaged and cause your toilet to drain slowly as well. They work to maintain consistent water levels in the tank and toilet bowl itself. Damaged fill valves affect the flushing power as well as how quickly the toilet drains after a flush.

You can find the fill valve inside of your tank near the ball float. This valve is somewhat delicate, and it is normal to have to replace them. Replacement is the only option when your fill valve is damaged, and it’s easy.


Plumber repairing toilet cistern at water closet

First, disconnect the water supply line to your toilet by turning it clockwise. Flush the toilet several times to fully drain it. Now, carefully pull the float ball out from the tank and mop up the remaining water with a sponge or rag.

Remove the valve nut with a small pair of pliers or an adjustable wrench. Pull the fill valve away from the supply line, and put the base of your new fill valve in its place. Tighten the valve nut, then reconnect it to the supply line.

Now, connect the new fill valve to the refill tube so that it will fill with water. Place the ball float back into the tank, and turn your water back on. Flush the toilet and see if this fix returned your toilet’s draining abilities to their former glory.

5. Siphon Jet and Rim Holes

The siphon jet and rim holes on your toilet help your toilet flush and refill. However, clogs can prevent them from draining, refilling, and flushing properly. These two components are the way that water enters your toilet bowl when they aren’t obstructed.

Siphon jets and rim holes can even prevent water from entering the toilet if they’re blocked. Less severe blockages tend to affect the draining speed and power more than the toilet refilling. Calcium is the main cause of siphon jet and rim hole blockages, but debris and waste can cause it as well.

It’s easy to overlook the siphon jet, and many homeowners only think to clean the rim holes. However, both of these parts of the toilet are critical in your toilet flushing and draining.


Make a solution that is one part bleach and ten parts water to clean your siphon jet. Take the lid off of your toilet tank and expose the overflow tube inside. Slowly pour the solution into the overflow tube, and it will exit through the siphon jet and rim holes.

Leave the solution alone for up to 10 minutes before you flush the toilet. You may have to flush the toilet a few times for the results to take full effect. Now, use a small instrument, such as a bobby pin or a piece of wire, to clear debris from the rim holes.

The rim holes get caked in minerals, and you need to break them up. Wear gloves to protect your hands and skin and wash your hands afterward. Flush the toilet when the holes are clean, and it should drain more quickly.

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Summing It Up

Clogs and mineral buildups are the most common reason that your toilet drains slowly. You can treat clogs with a plunger or drain snake, and you can break up minerals with vinegar. Otherwise, you may need to adjust the ball float in your tank to raise the water level in the tank.

A damaged fill valve can also prevent the water in your toilet from draining quickly. You can easily replace the fill valve and replace it to solve the problem. Toilets don’t need to be replaced when they drain slowly, and each of these fixes is quick.

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Nick Durante
Nick Durante

Nick Durante is a professional writer with a primary focus on home improvement. When he is not writing about home improvement or taking on projects around the house, he likes to read and create art. He is always looking towards the newest trends in home improvement.

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