I've wrenched on it pretty hard in the past, the design of the cap and the threads used just don't lock very tight. It always comes loose. But half of the problem I believe is it moving on the ground. Simply being strapped firmly to that cart and then being connected with a swivel cuff I believe will help.Thank you Robert86. Will do!! Mayne i can wrench it down a bit with a big set of channel locks or a filter wrench.