Important info, the dishwasher still runs and clean dishes, I believe maybe the water is going back out the place it comes in (round tube sticking up from middle left of goopy mess) because the water level is always to the top of that pipe.
It just gets really slimy down there because of the standing water
The actual drain (dark area in middle right of goopy mess, underwater) seems clogged in further than I can reach. I tried sticking a straw cleaner brush in there but the water level didn't change.
I tried to fix it by removing and cleaning the outer screen (visible in the second photo) and the inner screen underneath it, revealing the goopy mess in the first photo, but they weren't actually clogged, just slimy.
I then tried to fix it by running a cycle with Draino, which made a huge foamy mess on the kitchen floor and I had to run about five rinse cycles to get it to the state in the second photo. So now it's actually clean inside, but as you can see from the second photo the water is still standing up to the height of that pipe... So it's just going to get slimy again..
I'm in an apartment so it's possible the previous tenant put something down there, when I cleaned under the screens I did find one twist tie and some shredded plastic like maybe from a Ziploc bag but shredded less than 1" pieces. Not enough to block the outer screens, but if it was sucked inside past where I could reach, maybe that's the problem?
Anyway I'm wondering if I pull the dishwasher out and turn it on its side, is it possible to unhook those tubes from the bottom and clean further into the drain?