Black Mold in the Toilet Bowl & Tank

Last update:

The black mold you see in the toilet is a build-up of minerals, fungi, and mildew settling on the porcelain surface of the bowl. We often call them toilet bowl rings, but mold can also grow in the tank or around the toilet base.

Seeing it in the bathroom probably makes you uncomfortable, but the good news is that you can remove black mold quickly.

In this article, we will answer these questions:

  • Where does the black mold occur?
  • What causes toilet mold?
  • How to remove mold from the toilet?
  • Is black mold dangerous?
  • Does it indicate diabetes?
  • How to prevent it?

What Is Black Mold in Your Toilet?

Before we show you how to fend it off, it’s important to understand what toilet mold really is. It’s a discoloration indicating that you have mildew and fungus in your toilet. 

Although mainly black, it can also be green or orange. You shouldn’t confuse black mold with brown water in the toilet because they don’t share the same source.

Dampness in your toilet sets the breeding ground for mold spores and fungi, especially when you pair it with darkness and warmth. Your bathroom is the best place for forming black mold, along with sink drains, showerheads, curtains, etc.   

Where Does the Toilet Mold Form? 

Toilet mold represents the build-up of minerals, fungi, and grime on the porcelain surface of your bowl, but mold spores can occur in other places as well. You’ll often see it in the shower, kitchen sink, caulk, and many other places.

The problem with mold is that it gradually deteriorates the performance of the toilet while ruining that wonderful white color of your toilet. Besides that, black mold can form almost everywhere:

Option 1: Mold in the Toilet Bowl

The black mold frequently forms in your toilet bowl because water sits there around the clock. Stillwater is great at collecting waste particles, while mineral deposits add to debris accumulation.

Most times, you get to see the black ring around the waterline. That’s where the water keeps in touch with air, which boosts mold formation. Besides that, the black mold frequently pops up below water and under the toilet bowl rim.

The dark substance is ugly and harmful, so it can reduce the lifespan of your toilet

Option 2: Mold in the Toilet Tank

A toilet tank is another place where you’ll find black mold. Water constantly touches your tank — debris and minerals settle on the walls and bottom surfaces as time goes by. Grime also builds up around the toilet flapper to damage it. 

At the same time, it’s fair to say that homeowners rarely open and clean the toilet tank. You probably do it only when a bigger problem occurs, so it’s natural to find mold inside.

Option 3: Mold Around the Base of Your Toilet Bowl

Mold can also grow around the base of your toilet bowl, where water stands 24/7. It reveals that the toilet is leaking at its base, so you should search for cracks in your bathroom throne — functional toilets don’t let the water out like that.

Option 4: It Hides Behind the Tank

The last option is tricky because there are no visible signs of mold behind your toilet tank. It doesn’t mean that mold is not growing there — it only means you cannot see the black mold on the other side of the tank.

The back of the tank is hard to reach, but you can identify mold stains by standing right against the wall. Seeing the signs of debris should be easy because mold often spreads to the edges of the tank.

What Causes Black Mold in Your Toilet?

The black mold in the toilet is organic debris that grows when water sits in your bowl. Here’s what leads to the formation of the dark substance in your toilet. 

Hard Water

Water with a high mineral content is the main reason why you see a ring in your toilet. It contains more deposits than your toilet can digest, so they end up accumulating on the water surface. 

Stagnant Water

If you have hard and stagnant water, the toilet will surely suffer from mold and dark stains. Stillwater collects particles, deposits, and waste. All these elements pollute water and make the toilet look dirty.

You Don’t Use Your Toilet Often

If you travel frequently and use your toilet only a couple of times a week or month, the water doesn’t change as often as it should. In this case, you will probably see a toilet ring or mold in the tank. 

On rare occasions, you will also find mold underneath the toilet seat. 

Moisture and Darkness

Mold flourishes in dark and humid areas. Your bathroom represents a perfect generator of the black mold because of its dampness and darkness — not to mention all the waste that goes through it.

Rusty Pipes

Many toilets have metal elements and hoses that rust over time. Corrosion makes water dirty and stains the glazed porcelain surface of your toilet. It also affects the tank, its background, and even the base.

Cracks in the Toilet

Old toilets are prone to cracks and damages, and they might be leaking from tank bolts or other plumbing parts. Once again, it creates adequate conditions for mold.

The problem with cracks is that you can’t clean the black mold — it keeps forming until you replace the bowl.

How to Clean Mold From the Toilet Bowl?

You probably don’t want to leave toilet mold growing in the bowl forever, so it’s good to learn how to get rid of it. It only takes effort and elbow grease to do it, so make sure to follow these steps:

Step 1: Prepare Your Tools

You’ll need several items to clean the toilet bowl — rubber gloves, a face mask, goggles, a scrub brush, a bucket, a sponge, a spray bottle of vinegar, and baking soda. Make sure to get it all before you begin cleaning the mold.

Step 2: Ventilate the Bathroom

Toilet dirt and moisture create terrible odor, so you’ll need to ventilate the bathroom while working. Open the door and windows — it will replace the moisture with fresh air. You can also turn on the exhaust fan to improve ventilation.

Step 3: Get the Water Out

Now you need to get the water out of the bowl using a small cup and a sponge. Flush the toilet once, collect dirty water, and pour it into the bucket. When the bowl is empty, you can pour a drain cleaner to flow down and polish the pipes.

Step 4: Clean It With Vinegar and Baking Soda

The next task is to clean all the mold from the porcelain with white vinegar and baking soda. Mix the two elements using a small cup of each product — apply it to the stains and scrub them softly. 

You can also use the toilet brush to remove sturdy mold marks. Next, you should leave the substance sitting for 20 minutes before scrubbing it with the toilet brush one more time. 

Flush the toilet, wipe the bowl with a piece of cloth, and you’ll see that porcelain looks like new.

How to Remove Mold From the Toilet Tank?

The second lesson is to learn how to remove mold from the toilet tank. Start by closing the shutoff valve — you’ll see a knob behind the toilet, so make sure to twist it clockwise until it halts the usual water flow.

Remove the tank lid with your hands. After that, follow these mold removal steps:

Step 1: Pour Vinegar With a Spray Bottle

Your toilet tank contains many plastic elements, metal, and rubber items. To avoid damaging them, pour distilled vinegar inside the toilet tank (do not sprinkle baking soda). 

Remember to target mold stains, especially in the corners of the plastic tank. Some people use bleach for cleaning, but we believe vinegar is the best natural solution.  

Step 2: Scrub the Tank

Vinegar should do its magic for 20 minutes, but then you can start scrubbing the tank’s walls with a rag or a piece of old cloth. Do it gently because you might damage the tank or one of its smaller components.

Step 3: Pour a Bucket of Water

Take a bucket and fill it with hot water. Pour it into the tank to clean debris, but don’t use boiling water as it may soften and harm the plastic. When the tank is full, flush the toilet to see the stains disappearing.

If you still see mold in the tank, repeat the cleaning process to eliminate the strongest stains.

Step 4: Open the Shutoff Valve

The only task after removing mold is to put back the tank top and open the shutoff valve. That way, you will reinstall the tank and make the toilet functional again.

How to Remove Black Mold From the Back of the Tank?

Finally, you should use this mold removal trick to get rid of the ugly black stuff from the back of your toilet tank.

Step 1: Remove the Tank

Uninstall the tank by closing the water supply, flushing, and removing the fill hose beneath it. The hose has a metal thread nut that sticks it to the tank, so you can use pliers to unscrew it.

After that, find a couple of bolts that keep the tank steadily on the metal base. Twist them counterclockwise with pliers until the tank becomes loose. Now you can lift the tank with your hands because it’s empty and light.

Step 2: Clean the Tank

Put the tank on the ground, with its backside looking up. Use the same mix of vinegar and baking soda to clean the back of the tank — remember to leave the substance rest for 20 minutes before scrubbing it.

After that, it’s time to use cloth or rag to clean the remaining mold stains. When you do that, make sure to rinse the surface using clean water. Repeat the process if the tank’s backside is still dirty and messed up.

Step 3: Reinstall the Tank

The last step is easy as you only need to reassemble the tank after removing mold. Put the tank back in its original position, screw the tank bolts, and attach the fill hose. 

Then, open the shutoff valve and let the water fill the tank. Once full, you can flush the toilet to test it — there is no mold problem anymore, so it should work fine.

Is Black Mold in Your Toilet Dangerous?

Toilet mold can be harmful if you inhale its fumes or ingest it, but this rarely happens. First of all, you don’t spend that much time in the bathroom. Secondly, most stains are too small to produce toxic gas effects. 

However, the black matter in your toilet may harm people with allergies, asthma, and acute health conditions. Sometimes it can cause itchy eyes, stuffy nose, sore throat, or skin rash.

These issues occur rarely, but you don’t want to take any chances and play with your health. That’s why it’s essential to know how to remove mold from the toilet tank after flushing.

How to Prevent Black Mold in the Toilet?

You probably know that prevention is better than cure, so try to remember some of these anti-mold tricks and hacks.

Clean Regularly

First of all, you must clean your toilet regularly. Toilet mold grows faster in damp environments like toilet bowls, so don’t let it sit there for too long. On the contrary, use antibacterial products and tools to keep it clean at all times.

Ensure Proper Ventilation

Preventing mold also forces you to ventilate the bathroom frequently. It’s a no-brainer because you only need to open the window and let fresh air in. Another option is to install the finest exhaust fan to fend off moisture and dampness.

Fending off moisture is actually the main reason why bathrooms have fans

Use Dehumidifiers

Another tool that can help you is a bathroom dehumidifier. The best dehumidifiers make excellent tools for actively removing dampness from your toilet. How do they work?

They let you set the humidity level in the bathroom, which allows you to control moisture and change the setting based on your preferences.

Flush the Toilet Frequently

Another solution is to flush your toilet frequently to eliminate debris along with the human waste. It will prevent water from stagnating and developing awful dark substances. 

Flushing the commode several times a day keeps black mold at bay and stops it from growing in the tank.

Fix Possible Leaks 

Finally, you should inspect the toilet to pinpoint possible cracks and leaks. If you find any, do your best to repair the toilet or install a new model that works properly.

Does Mold in My Toilet Indicate Diabetes? 

Mold frequently occurs in toilets due to moisture and debris, so it doesn’t necessarily mean you have diabetes. However, people with diabetes have a higher sugar level in urine because they cannot process glucose.

It’s a perfect environment for mildew and mold.

The glucose-rich fluid serves as a natural ground for black mold. If you want to make sure everything is fine, you should test for diabetes. If you test negative, mold is coming from a different source.  

Do You See Black Stuff in Toilet After Flushing? 

Sometimes you’ll also notice black stuff in the toilet after flushing. It’s not as common as black mold, but you’ll also want to get rid of it. 

The problem usually occurs if you have rusty plumbing pipes. In that case, rust may form black stuff after flushing. Another issue may be that your supply system delivers hard water to the toilet.

Hard water contains calcium and magnesium minerals, so a little bit of dirt can turn mineral deposits into the ugly black stuff in your toilet bowl. But the good thing is that the cleaning process is the same as with black mold. 

The Bottom Line

No homeowner wants to see the black mold in the toilet after flushing because it looks ugly and even dangerous. Mold spores and mildew grow quickly in the bathroom, mainly because of debris and dampness.

They are a true nightmare, but you can prevent the black mold from evolving in the first place. Regular cleaning solutions and dehumidifiers keep the toilet moisture-free. Use them for prevention, and your toilet can stay clean for good.


How do you get rid of the black mold in the toilet?

It depends on the position of the black mold, but the only way to get rid of it is to clean the toilet. After that, you can use a few tools and methods to prevent further black mold growth.

What is the black sediment in my toilet bowl?

The black sediment you see in the toilet bowl is mold. The mold problem occurs when the water stagnates for too long — debris, mineral deposits, and other particles accumulate and grow in a moisturized environment.

Leave a Comment