On the sponge eh? They could be Psychodidae, drain flies. They’re about the size of fruit flies but usually appear fuzzier when magnified. Clear the flies out and seal off all nearby drains. If few or none return they’re drain flies living in the crud in your drain and the bleach didn’t do the trick, they can be persistent.
If so, try rounds of baking soda and vinegar, boiling water, mechanical action, etc to clean out of the drain, multiple times. Cap it off in between treatments and a good while afterward. If it’s a disposal, also run hand-fulls of ice through it running, works great at knocking loose the crud and won't hurt it.
On the topic of chemical insecticides, I work as a biologist but have no experience with using them anywhere near a captive ant colony as I am new to the hobby (an aside: there should be a name for a new pastime found in quarantine, some people are making homemade sourdough, I’m caring for “nuisance” insects and stockpiling their tiny wares). Anyhow, I know they can be lethal to insects in extremely minuscule quantities, you can reasonably suspect more so to captive colonies, and I would be wary of application in any shared airspace with my own fledgling colonies.
Edited by MysticNanitic, September 17 2020 - 10:44 PM.