I'd stay away from oxy-clean, as it will pit the surface of the inside of the keg if exposed to it for too long. Plus, oxy-clean is not a sanitizer.
Use iodophor or star-san to properly sanitize it.
Are you using a reconditioned corny keg? If its the first time I'd take all the parts and clean and soak them. Change the O-rings if that hasn't been done. Then do a pressure test.
If you've got a slow leak that CO2 tank will dissipate fast!
I just started this too so I'm no expert, but I do my homework before venturing to places unknown.
A little late cause I already tried my own method, but thanks for the advise. How do I perform a proper pressure test? I filled the keg with water, put abpout 20Lbs. of water in it and turned it upside down and nothing came out, is this sufficiant? Probably not. I recognize your user name, are you a fellow Jeep-aholic? Keith sent me over to this forum after discovering that I am a beer freek. I already met one jeepforum member over here, Harleysilo, pretty cool cat. Troy.
Your pressure test sounds good. orrelse is right...even a slow leak is unacceptable and will drain all your gas overnight.
If they're new kegs, definitely take them apart and clean the posts, the down tube, change O-rings and all that.
For general sanitizing, we use Iodophor, then put a little pressure on them to test, push the poppet down on the outflow so it gets purged with sanitizer, then flip it over and push the poppet on the inflow so it gets purged with sanitizer. Every so often, you should take them apart for a thorough cleaning. Being sure to rinse them immediately after they're empty is key to saving effort.