Proper connections and hoses should not leak, even when left on for an extended period of time.
Check ALL connections with leak detector/ soap solution, including hose lengths. Also check the cylinder valve.
A leak could be inside at the gas solenoid.
I check to see if a system is leaking by turning off the cylinder valve and watch the needles on the gage
to see if they drop. A leak tight system will show no drop (ever).
Also, in addition to the above, make sure to turn the valve on fully when you turn it on. This is a back -seating valve which will lose gas through the valve quickly, if not fully turned on.