I also think that we need to investigate the 725 system and see if the same problem can happen. Has the Manual Dump button.
I don't know if the tow companies know that they can "fix" the problem, just by airing up via the front air valve, without them or the coach owner knowing? Hence, when the coach is towed to a location and the tech can't reproduce the problem.....
Here is the control panel overlays: I think they can use a 610 panel or a modified 625
625: Notice there is not a manual dump button - see above sentence