I'm relocating a kitchen sink onto an island. The island is "down stream" on the 4" waste line from the existing kitchen sink. Does the island require a separate vent?

I'm relocating a kitchen sink onto an island. The island is "down stream" on the 4" waste line from the existing kitchen sink. Does the island require a separate vent?

Yes, all fixtures that have a trap will require a vent. A island vent, see image) is a special vent for island sinks. While this drawing says 1 1/2" i would pipe with 2". This drawing gives you a general idea but you don't have to follow it fitting by fitting, just follow the gereral layout. Good luck, Tom