Utility sink plumbing questions

I want to put a utility sink in my garage. The main reason is to have softwater hot & cold for car washing etc. I plan on tapping into bathroom plumbing in the basement and run pipes up and through the firewall just above the foundation wall into the garage. I have easy access to the basement bathroom plumbing in an adjacent unfinished utility room. I know how to solder copper and PVC pipes etc but have never done any drain/vent plumbing. The toilet and sink vent are shared in sort of an 'h' configuration. There is also a shower drain which is probably connected to that venting as well but I can't see that. The toilet vent would be the easiest and closest for me. I don't care about finishing the utility room so the pipes can run outside the wall cavity.
My question is where to splice the drain for the utility sink? Can I splice anywhere into the basement toilet (2") or bathroom sink vent (1.5") stack without causing problems?
What measures do I take when passing the plumbing through the garage wall (firewall)?
Garage can get cold enough to freeze I plan on putting some kind of manual shutoff/drain valve in the basement, but I would prefer some kind of automatic (passive) system where the pipes drain back into the house each time the water faucet is turned off or not in use. Does such a thing exist? (I know about anti freeze hose bibs but I do not want to use those if possible).
Do anti siphon valves need to be permanently installed on the plumbing? Or am I OK just using an external add-on hose bib anti siphon valve attached to the sink faucet?
Thanks
Kevin
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Kevin Ricks wrote:

First, you can't dump the sink drain into any vent. It should go into the main waste stack, but exactly where would depend on the layout of other fixtures. Too many unknowns.
Why not dispense with the sink and just have Hot/Cold frost-free sill cocks protruding from the wall.
Jim
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You may tap into the vent stacks for vents provided your tap in is above the drain. You can not in most cases tap into a vent for a drain line. "Wet vents" are not approved any more. There may be exceptions to that statement but I am not aware of any.
You can install stop/drain valve that would let you bleed the water from the lines at the end of each season. Whether or not anti-siphon is required for a garage utility sink is a local code issue. If you have a hose bib type connection then yes I believe anti-siphon is required.
Sealing around the pipes with a good layer of drywall mud or tight fitting metal flashing should meet most codes regarding the firewall part.
Colbyt
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Would it be OK to put in a 'cross T' at the basement sink so that the drains and vent are shared but no waste water is actually passing through a vent? This would be sorta like the 1st diagram given in the next reply by buffalobill. The difference being that the 2 sinks would end up on different floor levels. The drains would be connected at the same place about a foot above the basement slab. For the new utility sink I would either put in a 'cheater vent' or run a vent pipe up into the attic and connect to an existing vent. If that is all OK how do I protect the 'P' trap from freezing and/or drying out when not in use? Do I put a 2nd trap with vent at the basement connection as well?
Thanks Kevin

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