Home gnat problem

I had a problem with gnats inside our home. We have full house air condition with the evaporator in the attic. I bought a electronic fly swatter from Harbor Freight and it was almost fun hearing the frying sound as I eliminate the gnat on the windows as they flew toward the light. However, as the numbers grew I goggle gnats

and came to the conclusion that I needed to find the source. I close off our laundry room and found that room to be the source, I visit a exterminator supply and they suspected the laundry tub, I bought a liquid that coats the drain above the trap. I applied this to no avail. I was about to order a I decided to check the drain pan under the air condition in the attic. It did have a scum that the goggled articles suggested as breeding places. I plugged up the drain on the drip pan and poured a gallon on bleach in to the pan to soak for a while and I also sprayed bleach on the insulation in the air box. The house smelled like a indoor swimming pool for a while after I drained the bleach and turn the air back on. For a week now I haven seem a gnat.