I take my old potting mix and dump it in with the compost whan i do a new batch. i layerd about 70 cups that all got gnats during winter in the middle of the pile. now when i do compost i hot heep, and the soil in the cups has been bone dry for months before i added to the pile. the compost is almost ready and i took a temp of the pile which was 165 degrees. more than enough to kill most weed seeds and i am hoping any gnat eggs that may have been in there dormant. any advice or did i just mess up my whole batch of compost?

I do almost the same except the compost is in a bin. I have not noticed any gnats from a recycled compost. I have read somewhere that it is a bad idea to microwave compost to get rid of the unwanted elements so dont do it. But you can bake it in an oven, google for a proper temp

whats wrong with microwaving? unless you have those little fertilizer balls that might explode then there is nothing wrong with it. All it does is excite the electrons heating whatever is inside, thus cooking any life forms. Unless breakdown of the good stuff happens. Some nurseries do it while othersbuse steam.

I got two bins. I turn the heep every three days or so from one into the other. Keeps things cooking that way and I get finished compost in 1 to 2 months vs a year.

I wouldn't worry about fungus gnats eggs in compost.  They exist in the environment anyway, and there are no doubt things that eat them to keep their numbers in check.  And a hot compost in particular should do most of them in.  They become a problem when starting cutting indoors in a previously pseudo-sterile environment.  I had horrible fungus gnats two years ago, and many of my cuttings survived in spite of them, and then once they got outside, there is no more problem. 

Now, I wouldn't use said compost for starting cuttings indoors.  Then you're just asking for trouble.  Even a handful of eggs surviving can start an infestation indoors.  If you must do it, then yes, please sterilize in the microwave first.  That sounds pretty nasty to me, but should get the job done.

it seems banana attracts those gnats. after by some banana, i see them. once the trash is taken out, they are gone.