In reply to message posted by n30pc:
I made an adjustment. Didn’t seem to help. I removed the apparatus altogether and it still drains slow.
If that is the case, i.e. that you removed the plug from tyhe drain and it was still sluggish, you can have only these three problems (singly or in combination): 1) an obstructed or inadequately sized drain line (including trap); 2) an improperly sloped drain line; 3) improper venting.
There are no other causes of a sluggish drain that I know of in your case.
The only one that you can “fix” without replumbing is a clogged drain line/trap. You need to snake the line. If that doesn’t fix it, then you need to replumb the line.