watering with runoff systematically?

that is a lot of water, i give that amount to 20 liter pots .. you have gnats because your soil is too wet, i had the same prob in my first grow .. it took more then 2 months to get rid of them .. also made neem spray and all but there is only one solution = don't give them wet soil to breed in .. when you watered your plants pick up the pot to feel how much it weighs so you can learn when to water, you should water when you feel that the pot is light, try to water every 2 days in stead, in the meantime you need to buy a lot of yellow sticky traps ;) later on you can cover your soil with clay balls or plastic or fly traps so you give them less of a chance to get to your soil.. at one moment i had like 15 sticky traps all over.. you gotta catch em all ! ;) good luck have fun

As long as letting the pots dry out a bit then how you're watering is fine.