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Thick Black Gunk in Bathroom Sink Drain: How To Remove It

You wake up to a stinky smell in the house, and upon entering the bathroom, you are welcomed by thick black gunk in the sink drain. You have never encountered such a disgusting scene before and are worried about where the gunk might have come from. 

The black gunk in your bathroom sink indicates a blockage on the part of your sink drain that is causing the black sludge to back up into the bathroom sink. This blockage might result from the accumulation of minerals, skin cells, toothpaste, shaving creams, lotions, hair, hand soaps, phlegm, and bacteria on the walls of the drain pipes. 

Thick Black Gunk in Bathroom Sink

You must clear the blockage to revert your drain system to its operative order. In this guide, I will take you through various causes of this blockage and ways of solving the problem.

What Causes Thick Black Gunk in the Sink Drain

The sludge in your bathroom sink results from the build-up of one or combination of the following culprits:


When you clean, shave or comb your beard/ hair over the bathroom sink, some hair strands may break and fall into the bathroom sink. When flushed away with water, these hairs may bind with soap, grease, and other sticky substances. Then, they attach to the walls of the sink drains, causing a blockage.  

Bar Soap

A regular bar soap is made up of oil, colorants, and other chemicals that can resolidify to form a scum. This scum attaches to the walls of the sink drain. This accumulation reduces the water passage. It can also combine with other elements to clog the drain altogether.

Small Solid Objects

Small solid objects may accidentally fall and get trapped inside the drain pipes. Examples of these objects are needles, earrings, broken plastics, glass particles, and wires.

Then, other types of waste like minerals, soap scum, hair, oils, or shaving chemicals may start to cling to them. If the blockage goes unnoticed, it may block the entire pipe causing black sludge backup.

Mineral Build-Up

Is hard water a significant problem in your region? If yes, perhaps the black sludge in your sink drain is due to the build-up of minerals in a part of the drain.

Hard water may contain magnesium, iron, calcium, manganese, and other minerals. These may build up on the walls of your drains and form a hard mass that inhibits the smooth flow of wastewater. 

Over time, the mineral build-up may take over the entire pipe, leading to a clog. This may result in the black gunk backing up into the bathroom sink.

What Are the Warning Signs for a Black Gunk Buildup in Bathroom Sink Drains

Black gunk build-up can be detrimental to your health. And, since it is common in almost all sink drains, you need to familiarize yourself with its warning signs. This way, you’ll be able to prevent it before it turns into a major blockage. The common symptoms of black gunk build-up include: 

Sluggish Flow of Water

If the water in your bathroom sink drain is moving slower than it usually does, then something – perhaps, black gunk – must be blocking its smooth flow (if your bathroom sink is the only place that doesn’t have hot water, read here).

Unpleasant Smell

A foul smell may be a sign of a bacterial infestation. If your bathroom drain releases an unpleasant odor, it might imply that some organic substance is lodged on the walls of the drain pipes and that bacteria have started feasting on it. The foul smell might accompany the sluggish flow of water in the drains.

Gurgling Sound

A gurgling sound in your bathroom drain results when the air trapped inside the drain cannot be pushed out effectively due to blockage. If your bathroom sink produces such sounds, it might be the prime time to clean the drains.

How To Get Rid of the Black Gunk in the Bathroom Drains

Now, you understand the various causes of thick black gunk in the bathroom and its warning signs. The next step is to look at how to get rid of it should you find it in your bathroom sink drains. Below are my top tips:

How To Get Rid of the Black Gunk in the Bathroom Drains

Use a Plunger

The black sludge in your bathroom sink drain might have developed from a minor blockage on the drain system. It could need single or several pushes with a cup plunger. So, it is always safe to start with a plunger before proceeding to the next step.

Here are the steps to follow:

  • Cover the overflow opening in the sink with a wet cloth.
  • Place the plunger above the sink drain.
  • Fill the sink with water until it covers the plunger cup.
  • Plunge the plunger up and down in quick succession to deliver enough air to clear the blockage.
  • Remove the cloth and the plunger and allow the water to drain. If the water flows smoothly, you have successfully unblocked the sink drain.

Use Cleaning Chemicals/ Solutions

If the clog is too hard for the plunger to clear completely, you can do the rest of the job with a drain cleaner. Drain cleaners like Drano Max Gel Liquid Clog Remover and Liquid Plumr Clog Destroyer are famous for clearing all types of clogs.

For effective results:

  • Add the drain cleaner into the sink drain. Allow enough time as indicated in the instruction manual. This allows the chemical to penetrate and break the clogs.
  • Flush the drain with hot water and then use the water at room temperature to test if the blockage has cleared.

Use Baking Soda, Vinegar, And Hot Water

If you don’t have a drain cleaner, you can clear the blockage using baking soda, vinegar, and hot water. Follow this procedure:

  • Pour baking soda into the affected drain (the quantity of baking soda will depend on the severity of the clog).
  • Add 250ml of white vinegar into the affected drain.  This will cause fizzing and bubbling to remove the accumulation.
  • Allow the chemicals to react for at least 15 minutes as you wait for the water to boil. 
  • Pour the boiling water into the drain to clear the broken gunk.
  • Wait for a few minutes and then test if the blockage has cleared with room temperature water.
  • Repeat the procedure as required to clear the blockage.

If you don’t have the white vinegar solution, you can replace it with hydrogen peroxide and follow the same process. 

Use Baking Soda

Note: some of the above chemicals can be abrasive. It is advisable to wear protective gear to prevent them from contacting your skin and other critical areas.

What if You Don’t Have Any of the Above Chemicals?

A drain snake will do. All you need is to dip the snake auger into the sink drain until you detect some resistance, then rotate it until the clog dislodges from its attachment (if your auger gets stuck itself, read here).

If the clog doesn’t dislodge, you’ll have to remove it manually. To do this:

  • Unplug all the pipes beneath the sink from the drain system to inspect for any black muck.
  • Use a bottle brush or a wire hanger to clear any blockage.
  • Make sure you dispose of the waste in a safe place, preferably a trash can.
  • Replace the pipes into the drain system and pour hot water to kill bacteria and clear any remains.
  • Use room temperature water to test the efficiency of the drain.

If the water flows smoothly, then you are done unclogging the sink drains.

Concluding Remarks

The thick black gunk in the bathroom sink can pose health risks and interfere with your indoor comfort.

However, the good news is that you can easily clean it using drain cleaners or a mix of baking soda, white vinegar/ hydrogen peroxide, and hot water. You can also clean it manually using the procedure outlined in the article. 

Whatever your preferred unclogging procedure, always wear protective gear to avoid contacting the chemicals or germs from the drain. Remember also to clean and disinfect yourself after the operation. Your health is paramount.

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