Just in case this might be useful to someone, this is a design on Thingiverse for a Scubapro dump valve removal tool - Scubapro Dump Valve Tool by ic0n.
I have no idea whether this design of valve cover is still in use, but I see the 'official' tool is still made.
I have no idea whether this design of valve cover is still in use, but I see the 'official' tool is still made.