If I am draining my basement sink directly into the vent stack (bathroom sink already connected to same stack) do I still need to run a vent?

If I am draining my basement sink directly into the vent stack (bathroom sink already connected to same stack) do I still need to run a vent?

Every fixture that has a trap is required to be vented. Your basement sink is no exception. Pick the sink up with a 2" sanitary tee and come off the top of the tee with a vent. Cheers, Tom