I want to install a utility sink in my garage, not real sure how to run the drain though. I all ready have one major drain line and a hot and cold line, I just wasn't real sure if I needed to do sometjing special to make it drain right and I'm not sure where the vent is on it

Do you have a drain line or sewer that you can connecr to or do you intend to dig in a dry well? Let me know, Tom

Yes I have a drain line it's the one that drops down from the second floor

You can connect to the upstairs stack, however you must vent it. The easiest and cheapest way would be to install a AAV( air admittance vent) just after the trap, (see image) Good luck, Tom