What did you spray
WITH? - I had a CGA 580 Tee (to run both mig gun and spool gun off one tank) that leaked unless you got pretty serious about tightening, and on the
HIGH pressure side the gas tends to just blow LOW viscosity liquids AWAY before you see any bubbles.
More dish soap in water (if that's what you're using) or actual leak test liquid (yes, that's a REAL thing)
Radnor 8 Ounce Regular Temperature Leak Test Solution With Extension Tube: Amazon.com: Industrial & Scientific
We used it a LOT in industrial instrumentation, but it's expensive - several drops of Dawn liquid soap in a spray bottle works almost as well for home use.
BTW, solenoid valves in general tend to leak by if there's ANY foreign material around, as Mark mentioned - a good check for that (once you get your SERIOUS leak found/fixed) is to shut the tank valve tight, but do NOT bleed the torch side down after use - my MM252 (and everything after the tank valve) holds pressure for a couple of DAYS after use (with the tank valve CLOSED)
IF you're losing a full bottle overnight, there might be a speck or two of dust in your tank valve's female (or regulator's male) fitting - this is a metal to metal (brass) connection, it MUST be super clean with no nicks or it WILL leak.
With everything
EXCEPT Oxygen tanks I always crack the valve a bit (and blow it out with compressed air) BEFORE attaching a new tank. I also INSPECT both surfaces for any particles, nicks, burrs, etc, you never know who did what to that tank BEFORE you got it... Steve
Oh, another "check" I do (did I mention that us long-time instrumentation types are usually pretty OCD??!? :=)) - when I get a new bottle, after I SLOWLY crack the tank valve til I see the pressure SLOWLY rise on the HIGH pressure gauge, I GENTLY tap the gauge (they are mechanical inside, and tend to stick slightly) - then I put a small piece of electrical tape on the gauge face, ALIGNED with the pointer - this gives me a reference pressure on THAT TANK so I can see how fast it's going down. If it seems like it's changing too much, I'll RE-DO leak checks. So far, THAT little "quirk" hasn't shown that it's necessary, but ya never know :laughing:
...Steve