I think the easiest way to depressurise the whole system could be achieved through the safety valve (eliminating the need for a separate dump valve)
Cant as the dump needs to stay open in the pits, has to be something that will stay open on its own.

I won't allow a robot in the arena that needs to use a tool to dump it, if something moves inside or gets damaged, you have no way of making the system safe. Why cant you just move the dump, and run a small hose to it?