Stuck screw on bath spout

I'm not exactly sure what this part is called, but I have water coming out from the pvc pipe where the dishwasher drain hose goes into if I run the water in the sink for too long. I have a dual sink: right sink has the garbage disposal, left sink just a regular drain. Yesterday the water was backing up in the left sink when I would run the garbage disposal in the right sink. Clearly there was too much crap that collected in the left sink, thus the back up. I have fixed this problem before by using one of those mini sink plungers. I did the same thing this time and it was fine - I ran the water for a while in the right sink while running the garbage disposal and no back up. Later in the day though my wife was washing the dishes and had the water running in the sink and all of a sudden all this water started coming out from the pipe under the sink that the dishwasher drain hose goes into. I tested it out and I can run the water from the sink for a while (either sink) until the water starts to back up. Could the problem be that there is still some debris/small blockage that when the water from the sink is running on high and for a while it creates a backup? How do I fix this? Thanks. [attach]96269[/attach]

Shower head was leaking and so I attempted to fix it by replacing all fixtures and cartridge. Everything, considering it’s 18 years of age, came loose and apart with little to no difficulty. Likewise, all new parts, save the bleepity bleep bleep new cartridge, went smoothly. No amount of lubrication is assisting with installation. Gave up and reinstalled old cartridge using new O rings and the leak is more like a steady stream of water now. If I had an elephant gun my shower would be blown to smithereens! Anyone got an answer because YouTube is coming up empty!