I am having the drain fly problem in my house in New Jersey. The local pest company professionals identified these as drain flies.

The house is 25 yrs old and on a slab. It is a ranch style with no basement. I have two bathrooms one with a shower and a tub. It has been 2 years since I bought this house and I had to get it snaked 4 times by a local plumbing company so far. The first 6 months were OK. Since then I started seeing the drain flies. One thing I have noticed is that the numbers of flies are lot less in winter than in summer.

Based on the details can you suggest if a camera inspection will help to tell if the pipes under the slab are cracked or broken?

My local plumbing company tells me that something like a hair-line crack in the drain/sewer could be causing these flies and there is no way to find out using a camera inspection since the pipe is black.

I have tried all kinds of drain cleaners and bleach, but did not help solve the problem. I also smell sewer gases sometimes near one of the bathroom sink and the wasing machine drain.

Can you please suggest the path forward?

Thanks and really appreciate your help.

Sewer gas smell and flies leads me to think you have a trap somewhere near the smell that is dry. The flies live in the pipes and usually can't get inside the house unless the water level drops in a P trap and lets gas in. Do you think your washing machine is trapped correctly or is it possibly going into a pipe in the wall that goes straight down to the drain line. Try bleaching the heck out of the pipe the washer goes to, not the rubber part attached to the machine. Cap that pipe for a few days with plastic wrap and see if things improve. If it improves then there is your source of both problems. You can create an external trap but you'll need 2" pipe to handle the pressurized discharge of the machine.

Are you sure they are drain flies? I thought I had them, too, but then I started noticing they were everywhere in the house, not just by sinks. Turns out I had fungus gnats. They look very similar to the drain flies.

Fungus gnats are actually easier to get rid of, as they breed in potting soil. Airing out the soil, or getting rid of it, eliminates the problems.

We will still have the mysterious gas smell. Please look into the washer drain pipe.

Because I have houseplants I brought a couple plants in the winter and soil.. will get rid of them... Pray for me that this works...