Gnats coming from dryer hookup nonstop

I live in a ground floor apartment that is only 2 years old and have a dryer hookup on the floor of my bathroom but I do not own a dryer. There is a constant stream of pretty powerful air constantly coming from it but also, tons of gnats. It’s never more than a few at once but for months now I would kill 2 or 3 gnats, then 2 or 3 would replace them the next day. I do not have this issue with the shower and the apartment did not come with a cover to put over this hole so I can’t seal it off. I tried cutting out some plastic to the hole size and sealing it with duct tape but the constant stream of air eventually moistens the tape and the gnats start coming through again, just after a couple days. There is no way to get access to the system, it’s just a hole where the hookup is. The inside pipe goes sideways so in order to flush it out I have to constantly fill up the hole with water, 1 cup at a time but it doesn’t help anyway.

It’s not a total nuisance, I never see more than 1 or 2 gnats at a time but they are seemingly replaced a few hours after I kill them so there hasn’t been a day since I moved in that I haven’t seen one flying around. This has gotten to be extremely annoying and I have no clue what to do. It seems like they laid eggs far into the pipe where I cannot reach and this has been an issue since I moved in. Gnats are just part of my daily life and I don’t know how to fix it.

Any suggestions would be wonderful, as most I see are for shower or sink drains, which do not have this issue for me.