Bleach in the Drain? Stop. It Doesn't Work.
Pouring bleach down the sink? Stop. It doesn't work. Learn why drain flies survive bleach and how to use enzymatic gel to actually kill the nest.
I walk into commercial kitchens and see guys pouring gallons of bleach down the floor drains. It smells clean, sure. But the next day? The flies are back.
Here is why bleach fails.
Drain flies (those fuzzy little moth-looking guys) lay their eggs in the organic slime that coats the inside of your pipes. It's a thick, gelatinous muck.
When you pour bleach, it runs right over the slime layer like water off a duck's back. It might kill a few larva on the surface, but the eggs protected inside the slime are totally fine. The bleach flows past in seconds. The slime stays.
You have to eat the slime
To win this, you don't need poison. You need biology.
Use an Enzymatic Cleaner (Bio-Gel). It's a thick goo filled with bacteria that actually eats organic matter. You pour it down at night and let it sit. It clings to the pipe and digests the slime.
No slime = No food for the larvae = No flies.
The "Tape Test"
Not sure if the flies are coming from the sink or the shower? Stick a piece of clear scotch tape over the drain opening (leave a little airflow gap) before you go to bed.
Check it in the morning. If you find flies stuck to the tape, you found your breeding ground.