We just had the same problem with back-to-back sinks. No amount of plunging solved the issue (and yes, we had both overflows and the other drain completely blocked). We were finally able to snake out the clog using the method described by hkstroud above, without having a drop head auger tip. Our pipes did not have to be cut; we were simply able to unscrew the pipes directly at the wall and could see all the way through from one side to the other. However, we didn't have a piece of PVC pipe to redirect the snake, so we just used a broom handle in the same manner. Worked like a charm, and our drains are finally flowing properly.

Hi egeoffreyand welcome to The Plumbing Page on AMHD.
You piggybacked on a 1 year old dead thread so I gave you one of your own. Before you post look in the upper left hand corner for the date..
Glad you got your clog and thanks for the up date, Tom