drain slope

Hey everybody, I am replacing a horizontal six foot section of 1-1/2" copper drain pipe in a wall with 1-1/2" DWV PVC. The holes through the 2x4 studs are 2" and round. The section of copper I'm replacing was almost level (1/4" in 5 feet), which led to corrosion, which is why I am replacing...

We recently installed a new kitchen sink and did the drains ourselves. However, after running the water for about 4 minutes it starts to back up in the sink. We installed an AAV and snaked the drain(and took it all apart). We know there is no blockage on the "inside" part of the pipes. Could...