We're having a problem with our new double sink backing up after just a few minutes of washing dishes and it seems to be getting worse. We just switched from a single sink to a double and I guess it may not have been installed properly? Our old set up occasionally was slow draining because the pipes leading from the sink had an unusually high way to go up after the P trap, before reaching the drain pipe that goes down into our kitchen floor -- so when we changed the sink, we also had this adjusted to connect lower down, thinking this would improve the drainage.

The pipes from the double sink connects to a pipe that comes in at the wall at about 2 feet high and then drains to the floor (which is pretty continuous, nothing that looks like a vent) -- we live in a large apartment building so I assume this is our vent pipe and would think that if it worked well enough with our old sink it should work with this one.

But as you may be able to tell, we're new to all this. I'm feeling unsure of having the guy who put in the sink come back to fix it if he may have been the cause of it in the first place, so your suggestions would be appreciated! Thank you!