Before I start trying to answer your "air leak" question, it's EXTREMELY IMPORTANT that you take steps to replace your temporary fuel supply system with a properly installed and secured/plumbed tank and fuel supply line. One of the first and biggest rules we remind all Stovebolters about is "SAFETY COMES FIRST"!!!
It's considered ok to temporarily use a well secured tank and supply line like you have as a means of starting/running the engine when temporarily testing/servicing/tuning the engine or a short move from yard to shop, etc. However, such set ups are not encouraged or suggested for use in normal "work" operation of the truck (like what you are showing in your post) as it poses a significant safety and fire hazard.
While you are working on resolving whatever problem has come up with your "air leak", please rectify the fuel tank and supply line issues before putting your truck back to work. Your family/significant other/whatever will thank you for working safely and coming home at the end of the day un-scorched/uninjured!
Stovebolt does not condone, encourage or approve the use of unsafe practices or use of equipment!
PS - Did you not set/check your parking brake was engaged and functional before hoping out of the truck to operate the dump bed? This too is a MUST DO every time you operate your truck and dump bed for your safety and those that may be around you. SAFETY FIRST - PLEASE
