Trap arm slope

I just read in the pipe dope thread that the lav trap arm should have a slight slope towards the trap. How critical is that? I just installed my double sink drains and I had the trap arms slope away from the trap.

Note that in a different double vanity installed by the builder 18 years ago, the trap arms slope very dramatically away from the trap and we haven't experienced any problems. Thanks.

I don't know why it would slope towards the trap.....that would cause problems.

Traps arms should be sloping at a 2% grade "down hill".
That is the same as 1/4" per foot.

Ideally, give it a bit of a slope downward toward the drain. On very short lengths, even level will work OK, but never try to make water run uphill under gravity.

slope

IF there were a reason to slope UP from the trap it would be for any piping between the trap and the sink. AFTER the trap the piping slopes downhill.