On Sat, 14 Apr 2012 20:37:10 -0500, Puddin' Man
wrote:

Just an old 2-basin kitchen sink. We ripped the old copper drainpipe out
maybe 4 years ago, installed ~ 5' of pvc.

Drain runs slow. Works, but obviously only 2/3 of capacity. I start
with bakg soda and vinegar, then some crystal Drano, then the pot of
boiling water, then the plunger. No noticable effect.

Any ideas?

Yes, a snake. Sometimes you get a clog that the chemicals just won't
move. Put a real wire snake down there and find it. The chemicals
are AOK for the trap, but the clog may be a few feet down the line.