Diane from Orillia, Ontario writes:

I keep cleaning out black guck from the top of the drainpipe in the bathroom sink, also around the lip of the drain in the bathtub.  I have noticed this for about 8 months (about the time I switched from regular cleaning products to environmentally safe ones).  My house is about 60 years old. Do you know what would cause this?

Hi Diane, thanks for the question.

My house is about the same age as yours, and I have had a similar problem with my bathroom drains.  What you are experiencing is a buildup of what’s known as biofilm.

In essance, you have bacterial colonies growing on the inside of your pipes.  As bacteria grow, they produce a slime or guck as you describe it.  The slime contains the bacteria as well as all of the secretions that the bacteria produce.

Bacterial biofilm grows in a similar fashion to sea coral.  It will grow out and up to take every viable surface area it can.  it also grows on top of itself getting thicker as time goes on.

Since your house was built in the 50′s, you most likely have galvanized steel drainpipes.  These drainpipes contain iron, and allow iron reducing bacteria to grow under optimal conditions.  Iron reducing bacteria are especially adept at forming biofilm, and can grow quickly.

As well, other guck, crud and objects can add to the growth of this biofilm. Hair tends to get trapped in bathroom plumbing aiding the biofilms growth.  Another issue is shaving cream, which forms a sticky foam in drainpipes, that the bacteria love.  Think of this hair and shaving cream as condominiums for bacteria, giving them more surface area to procreate in, as well as other nutrients.

It is likely that your previous cleaning products contained bleach, harsh acids and the like keeping your pipes clean by keeping the biofilm at bay.  When you switched to greener cleaning products, they no longer disinfected your plumbing and allowed uncontrolled biofilm growth.

There are several ways to deal with this problem.  If you plan to do some plumbing in the near future, it would be a good idea to replace your galvanized drain lines with ABS plastic lines.  This would eliminate the iron reducing bacteria as there would be no iron for them to feed on.

To deal with the biofilm in the plumbing you have now, you must do two things:

1. Physically reduce the amount of biofilm and hair/shaving cream etc. in your plumbing
2. Disinfect the plumbing to keep the biofilm from spreading.

Look under your sink.  Most sinks have what’s known as a p-trap underneath them. It’s a gooseneck assembly designed to keep water trapped in the pipe so sewer gas cannot escape into your house. Many have a clean out assembly in the bottom. If not, the assembly usually has screw off unions so you can remove the whole thing. When you do this be careful, there will be water that will come out of there.

Your local hardware store will have what’s called a plumbing snake.  It’s a coiled up wire with a screw like device on the end, and a handle so you can turn it.  You can use that to clean out much of the guck from your drain lines.  Make suer you have a bucket underneath, when you pull it back it will bring black guck, hair etc. back with it.

Next, you need to disinfect the plumbing.  Put the p-trap back together.   Take a cup of bleach and mix it with a bucket of warm water. Pour this slowly down the drain.  This will kill the surface bacteria, stopping it’s ability to reform the biofilm.  A weak chlorine solution should not harm the septic system as it will react with the biofilm and galvanized pipe and should be used up before it gets to far in.  Just make sure it’s a dilute solution, as straight bleach can harm a sewer/septic system.

That should stop the black guck from reforming. Make sure you disinfect your drain lines at regular intervals.  As disinfectants can only kill surface bacteria, the bacteria underneath the biofilm will work their way to the top in a few weeks.

I hope I’ve been of help. Please do not hesitate to write in again should you need further clarification or have more questions.

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