new setup

So I recently bought a new used keg and finally got my co2 tank filled and just waiting to fill with beer. My question is I wanted to put pressure on and check for leaks. I set psi to 10 and it was like the gas wouldn't stop. I'm guessing becase keg was empty so would have to use a lot of gas to fill it. Should I fill keg with water and try checkin, as to not burn up as much co2 or just let the empty keg fill. Also what is best way to clean system? Keg looks spotless inside so maybe just run little starsan through it or should I really clean it.

Both of your solutions are solid.

You can even push the Starsan water through your beer lines to clean them. One thing I would add, is to spray some starsan water around all of your connections, as well as your keg lid. If you get bubbles, you've to a leak.

Thanks. I prob just pump star san through it for awhile and I have a soap water mix to check leaks

One more question when i need to purge the keg do I push the relief down with screwdriver or do I have to buy a special poppit to put in its place little confused. Thought I could just push it down but I can't.

For the kegs I've got without pull up pressure relief valves, I tend to use a spare Gas QD to vent kegs, though that is using pin lockss.

Gotcha yea guessing I would have to buy a new lid to put one of the pull up reliefs in.