That was one thing I hated when I lived in my apartment--many people didn't clean up the poo!!! Usually the ones with the bigger dogs too!! A very sweet older couple who had a bichon ALWAYS carried a big grocery bag with them--I used to laugh--I don't think they needed a bag quite that large. Maybe once or twice I forgot a bag, but I either went back out and picked it up, or scooped it up with some leaves or something I found on the ground.
With a notorious poop muncher *coughKitocough*, I always knew where the spots were. It's funny though, after a certain woman and her collie moved out, there were a lot less.

Good luck dealing with this--I cannot believe someone lets their dog pee in the hallway--that is absolutely disgusting!!!