I always go through the release of pressure before I detach my grapple, but it is good odds that the grapple will build pressure just sitting there. SO, finally took the time to build my version of a release tool, hopes it works.
The old farmer way to do this is bang the male tip onto a piece of hard wood or metal, which will push in the ball and release the pressure. (plus get some oil on your pants. )
The best solution is the female coupling where you insert the the male coupling then rotate a lever that pulls the two together even under pressure. I know Steiger tractors had this type, not sure who made them.