We had our kitchen remodeled about 7 years ago - our main sink was relocated and we added a prep sink in the island. Our main sink is vented via a pro-vent style vent (its not tied into the vent stack up to the roof) and the prep sink is not vented at all.
Both sinks are tied into same drain line downstream in the crawlspace.
Last weekend I noticed our garbage disposal in the prep sink was all rusted out inside and water was leaking down through the motor so I had to replace the garbage disposal ($100 after 7 years?).
I was wondering if the lack of vent on the prep sink could have caused water to not drain properly and hold water in the disposal which cause the premature rusting.
Both garbage disposals and In-Sink-Erators and the main sink disposal is still shiny and new looking inside (no rust).