Mystery leak in drain line under basement floor

For two months, I have been trying to find the source of a drain fly infestation in my basement. I finally discovered that there is water in one of the clean-outs of a drain line under the basement cement floor. The flies are clearly breeding from this source (about 10 flew out when I dug out some of the soil below the clean-out plug). The clean-out pit is cement on the sides, but has a mostly dirt bottom.

There is a sink about 2 ft. from the clean-out. When I put food coloring down the drain of the sink and run the water, about a minute later, the water in the clean out pit turns the color of the food coloring so I know that I have a leak somewhere. I have to suck the standing water out of the clean-out pit with a shop-vac to get the water to flow into the clean-out. The water level in the clean-out does not appear to go up even when the sink is on full.

Now here is the mystery part. I had the line inspected today with a camera. We looked at the main line, the line connecting the sink to the main line and another line further up from the sink. There were no OBVIOUS leaks or cracks or standing water. My food color test proves that there is a leak, but my only guess now is that it is small and/or possibly under some of the scum inside the pipe (these are 80+ year old cast iron drain pipes).

I would like to get an opinion on next steps which I see are as follows.

1
Have the line inspected by another drain company (the first was Roto Rooter). I was thinking that power washing the inside of the pipe may help remove some of the scum to show a leak?

2
Try and seal up the clean-out with hydraulic cement. This will not fix the leak, but it may stop the drain fly problem since they will be “trapped†under the slab. My guess is that they may find another way out elsewhere.

3
I am also considering having the pipes lined with an epoxy liner. This was just demonstrated on “This Old House†and I would think that this would fix any potential hair-line cracks. I do not know the cost for this procedure, but figure it would be reasonable to just do 10-15 feed of pipe since I am fairly sure the leak must be close to the clean-out due to the speed at which the food coloring shows up.

Thank your for your help on this strange matter.

-Justin

You may first try cleaning the inside of the drain pipes out with a good enzyme-based drain cleaner like DrainCare. It will eat out all organic gunk, and perhaps expose the leak. (My guess is that it would most likely be at a connection.)
To use DrainCare, you run warm water down the drain, pour in DrainCare as directed, let it eat overnight, and then run hot water down it to flush the loosened gunk down. I usually start the hot water with a kettle of boiling water.
If one time doesn't clean it well enough, then you may have to do it more than once, before hiring another camera inspection.
Good Luck!
Mike

I think, and may be wrong, that having the pipe lined is not as inexpensive as you think.

drain

1. Power washing will not remove the encrustation inside the pipe. That is rust and is as hard, if not harder, than steel.
2. If there is water in the opening and its level does not change then it is probably a floor drain. A cleanout either does not have water in it, or the line needs to be snaked if it does.
3. The major cost of relining the pipe is setting up the equipment and preparing to do it, and that costs the same whether it is 10' or 200'. And before they do it, they have to scour the inside of the pipe so they do just replicate the interiors's uneveness.

Thanks

Thank you for your responses.

I was able to find the company from the "This Old House" episode and they are going to come by for a second look at the pipe with a color camera. I will give the enzyme cleaner a try before them come to hopefully get some of the gunk out of the pipe. I expect as well that the leak is from one of the joints. I guess the wost case is that I just line the entire pipe. Let me tell you, if you have ever had to deal with drain fly issues in your house you get to the point where you are willing to do anything to fix the problem.


hj,

There is a floor drain "up stream" from the clean-out. However, the sink where I ran the food color test drains right next to the clean-out so I am fairly sure that the floor drain is not part of this issue. The water in the clean-out is coming up from the dirt at the bottom of the clean-out which is just below the level of the pipe. I am not sure why the bottom of the clean-out pit is dirt other than the fact that "they do not build them like they used to". The house was built in 1920.

It might be cheaper just to cut the slab and replace the section of pipe instead of trying to fix it with a liner....

Update:

Received a second opinion on the leak and the contractor is 95% sure that there is a bad joint about 2 ft. down from the clean-out which is the cause. We are going to take a bit of a "belt and suspenders" approach and replace some of the pipe by jack-hammering up the floor and also re-line the rest of the pipe which is under the finished portion of the basement.

Question:

He has also suggested to replace another 10ft of pipe (and a floor drain) which are "up stream" from the leak. While there is no known issue with this pipe, I would agree that while you are digging up the floor, may as well cover your bases rather than coming back to a potential issue. Any opinion on "fixing something that is not broken"?

-JT

With old cast iron, sometimes it is best to bite the bullet and replace more than you "have to". Sometimes you will create more leaks while disturbing the adjacent pipe while repairing the existing leak.
If he is replacing the cast with plastic, just make sure he is using the aproved transition fittings (labelled as CI to plastic etc) as the standard CI bands will not seal properly.