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  1. #1
    Join Date
    Aug 2008

    Default Odd black mold like substance in sink drain

    We recently completed a remodel that included replacing a standard water heater with tankless model. Post the remodel we noticed a black, almost rubbery substance "growing" in one of the sink drains. There are two separate sinks in the bathroom and only one with this issue. The first time I took the p trap out because the sink wasn't draining well and the black stuff had formed almost a seal across the drain pipe. We washed all affected areas thoroughly with bleach and reassembled but it has come back. For reference we live in Dallas, TX. Anyone have any idea what this could be?

  2. #2
    Join Date
    Aug 2007
    The Great White North

    Default Re: Odd black mold like substance in sink drain

    Just the other day I had to clean out my bathroom sink drain as there was a bad clog.

    After removing the "P" trap and cleaning out the piping there is usually lots of black slimy crud ( technical term ) built up inside the piping .... this is typical.

    Here's one thing that I've noticed .... if shaving cream is being used while shaving this seems to contribute to build up inside the drain pipes. Usually this will be noticed on a pop up sink stopper as well.
    That might explain why one sink is more so than the other.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  3. #3

    Default Re: Odd black mold like substance in sink drain

    So how do you get rid of this stuff? In our old pedestal sink I see it in the drain, the stopper if you pull it out, and in the overflow slot. Seems like maybe a high pressure hose attached to the faucet to flush it out followed by some diluted bleach sitting overnight, then flush again might do it. Any ideas? This must be getting in the air and can't be good for us.



  4. #4
    Join Date
    Dec 2009

    Arrow Re: Odd black mold like substance in sink drain

    Any Luck getting rid of this? I had the rubbery sludge in the bottom of the overflow and used a stopper under the drain. Then filled with water and and used a plunger to force the material up and out of the drain.. Still got mold at the top of the overflow though.. Anyone with any luck fixing this problem??



  5. #5

    Default Re: Odd black mold like substance in sink drain

    You are describing a biofilm.

    This is a contamination. Once established it can be difficult to control, especially if it is abetted by an improperly (not draining properly and scouring properly) building drain, fixture branch, trap, etc.

    The flora can and often do make persons ill due to splashing, aerosolization, direct transfer, etc.

    Often a singular event such as a contaminated floor drain, a singular backup, clog or flood can introduce the slime forming organisms and the bioslime/biofilm contamination process.

    There is a particular approach often used regularly in food processing facilities which includes brushing and scouring the entire DWV, building drain and sewer, and total decontamination of the entire zones but rarely employed in a residential setting.
    (First provided clickable link below discusses the process, there are many other authoritative resources you can consult).

    Note, regular household products containing chlorine will not do the job of decontaminating from bioslimes.

    A while back ZEP introduced a foaming drain cleaner for bioslime. Supposedly it works reasonably well without the need to brush or scour the system for it to work. I have not researched the claims nor investigated the process since its introduction. (See Second and Third provided clickable links below).

    Once cleaned, preventing recontamination especially from the sewer is essential. Maintaining a regimine for a time period of sanitizing the system would be a good idea. If your water supply is the source of the contaminating organisims, this should be remediated and the entire potable water system decontaminated (often involves copious amounts of hydrogen peroxide and other methods). If your traps, drains, etc. are not scouring properly (pitch, drainage, proper venting, etc.) you will continue to develop problems as well; removing the biofilm/slime and disinfecting is essential. Even if you are on a public water supply I highly recommend you invest the few dollars to have a certified lab test samples taken from multiple taps at your home and your water heater drain as well as at least one exterior hose bib to determine if a source or a cross contamination of your potable system has/is occured/occuring.

    If your building sewer empties to a private sanitary treatment system (septic for example) there may be an issue with the system drainage and/or function; if public may be an issue with your pitch, fall, etc.

    These are the three clickable links promised above to get you on your way learning about biofilm bioslime contamination and removal from DWV, Building drain and Building Sewer (I suggest you do your own research before forming a procedure or action list):


    This is a pdf document from Zep (manufacturer of cleaning supplies mostly commercial, some hospital grade, and some residential):


    This is an industry media article about the new Zep product:


  6. #6
    Join Date
    Dec 2009
    Casper, Wyoming

    Default Re: Odd black mold like substance in sink drain

    I would try some good old baking soda and hot water and see if it removes the black substance. Or, perhaps it's time to contact the plumber who installed the water heater and see if he knows what is going on.

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