I'm brainstorming some ideas here

Bought a house with a detached garage. I'm using it as a wood shop and would like a slop sink out there. No water running to the building currently, but I'm thinking about upgrading the electrical service to give me more than 30 amps out there and while I've got a trench I want to run some water. Problem is, its not a heated space, and I don't have plans to insulate and heat it.

So I want a sink that I can use year round in an unheated space. Is this possible? I've never heard of doing this so I'm guessing there's no good way to keep it from freezing...

The water line would have to be buried at least 42" deep and you would use a freezeproof yard hydrant at the sink for the faucet.

The sink drain may be more of a problem than the water supply.

and you would have to put a cup of antifreeze into the sink trap after each days use (in freezing weather)..

What makes you think he would connect it to a drain and need a trap?

The drain could possibly be routed to a foundation or gutter drain system. It will likely be neither an easy or inexpensive project but it is doable.

A year around sink with water... and no continous heat? You can bury a water line deep but water in faucets, freezes and expands.

Each time you are finished in the unheated garage, you will have to turn the water off in the house... to the garage and drain the faucet and drains.

Otherwise, You are in for a dandy lesson in winter plumbing... and Nature's Law.

Best Wishes

your using this space to work in, increasing the electrical feed, no heat? borrow the cash from your brother, insulate & heat, bring in water. like the other fellow said, use the down spout for a drain. a little hand washing shouldn't be a problem. the main thing is keep your mouth shut about this project.