If you notice that your sink drain is discharging some black stuff in the form of debris, stop using it immediately. Determine where the debris is coming from before using the sink again.

The black debris may be as a result of a backing up sewage. It can cause serious damage to your house if left unattended. Moreover, such debris is a serious health hazard.

sink drain black sludge slime

Biological Film

Most people wash biological matter down the drainage system when using the sink. Biological matter includes materials such as soap, oils, and hair.

These materials often cling onto the interior surface of the drainage pipes, thereby creating layers of film. The film creates a perfect environment for bacteria to grow.

As bacteria grows, it makes the film appear black. The film may become loose when pouring harsh substances such as drain cleaners down the drainage system.



Whether your sink drain is partially or completely blocked, a portion of the blockage might loosen and backup through the sink drain.

In case your sink is taking more time to drain than usual or water is not draining at all, then you probably have a clog to deal with.

The black matter coming out of your sink drain might be caused by a clog. Most clogs comprise of biological matter.

As such, bacteria thrives in the clog, thereby turning it black. You can use an auger or plunger to clear the clogs and stop the black debris from backing up through the sink drainage.


Vent Pipes

If the vent network connected to your sink drainage line is obstructed, wastewater may backup and get discharged through the sink drain.

Branch drain pipes are usually connected to the main vent or branch vents. If the vent network is blocked, there will be poor ventilation in the drainage system. Consequently, wastewater may backup and get discharged through the sink drain opening.

You’ll need to climb up your roof to access the vent opening and remove the obstruction. Clearing the obstruction is best done by pouring water into the vent at high pressure with a hose.


Sewage Backup

Sewage backup can also make the black debris get discharged through the sink drain opening. Generally, sewage backup settles on the lowest part of the drainage system.

In case there’s a sink on the lowest floor of your home, then it’ll be among the first drain openings to discharge the sewage backup.

Sewage backup might be due to an issue with the main sewer system. In this case, you’d need to contact your local sewerage company to assess and fix the problem.

In case the septic tank is full, it’ll have to be emptied. In case there’s a stubborn clog between the main sewer system and your home, then contact a plumber to clear the clog.


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