This question is in regards to the Washington D.C. area.
Is there a certain angle in which my drain pipe from my sink needs to be to connect to the main sewer drain in the house? I had a plumber come in & tell me my drain line was at to steep of an angle. That doesn't make sense to me, but I'm not familiar with the plumbig building code.

The first thing that comes to my mind is when the drain pipe goes horizontally across inside the wall and then turns directly vertical to go down. I wonder if a 90 degree turn to go straight down is too steep. The code calls for a 'minimum' fall of 1/8" for 3" pipe and above and a fall of 1/4" for 2" and below. If directly vertical is OK what angle do you call too steep?