Kegging help

[manfield8]

I have brewed a few beers over the last lets just say 5 years. This last year I decided to get some kegs instead of always bottling the beer, so I went and grabbed a keg, then saw a craigslist find for a keezer and 4 more kegs, then my brewing/work colleague found someone selling a bunch of 5 gallon kegs for $25 so I decided to get a few more to finish my collection. Anyways this past year I have brewed more than my previous 5 years combined because I don't have to mess with bottles...The kegging part has been going fine but what I cannot seem to get right is the force carb of the keg. I have 2 5 lb CO2 canisters one came with my first keg another with the keezer haul, I have went to a localish gas exchange place (Linweld) to exchange my tanks, but I have had to do it way more than I should. I just cannot seem to keep the CO2 in the keg or the canister when trying to carb up the keg. I have done everything I could think of doing to try and find or get rid of leaks but I just had a keg on CO2 for about a week and today when I went to take a look at it saw that the regulator said 0 for pressure...this one I changed all O-rings in keg, was a brand new regulator & hose and fittings for CO2 line, after hooking up tank to keg/regulator I sprayed so much water/sanitizer from my spray bottle to check for leaks/bubbles which I could find any. So I guess what I am asking the community is there something I might be missing as far as where a leak might be coming from? I just hate to keep throwing $20 of CO2 down the drain.

 

[camonick]

Do you have one of these nylon washers between your regulator stem and CO2 tank valve?

and these nylon washers (fish eyes) between all metal to metal flare fittings?

 

[IslandLizard]

You definitely have a leak!
A carbed up keg should stay carbed and only use some gas when you pour a glass.

Have you opened and checked your QDs? There's a small screw lid with a screwdriver slot in the top of QDs. Underneath is a small flat o-ring that seals the QD. If it's deformed or loose, it will leak.

The other place is the o-ring on top of the keg post. Keep it well lubed and replace if suspicious/worn. Gas can leak almost unnoticed along that o-ring when the QD is attached. That's the only seal to keep the gas from leaking there.
Also make sure the post is not damaged, as that may prevent a positive seal too.

The keg lid is another area. So are the rubber o-ring seals underneath the dip tubes. Then there's the PRV.