orangetrader wrote:

I need to route a 3" PVC drain pipe from my garage (from the washer) to the
kitchen drain.
.....

Why 3"? 1-1/2 or 2 (max) would be more typical for a washer.

My first question is about the relative heights...can you get enough
drop to go 6' to an elbow and then another 4' to the down stack?
There's going to be a problem perhaps in getting good flow. Also, what
about trap and the vent?