Of my last four propane tanks, I've had this problem with two: I turn off all five burners on my grill and obviously leave the tanks valve closed, but as soon as I screw the regulator onto the tank valve, there's a hissing sound of gas and the accompanying smell.
You will need to get your van up on ramps, or use your Lynx Levelers or something safe to give you some more working room.
Depends on what this is.
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