Best is to rinse the DPV with the key installed and then remove it. It does not hurt anything to rinse the pins if they get dirty or exposed to seawater, but there's no reason to rinse them if they are already clean. There's also no reason to rinse the key separately, except if you accidentally get crud or seawater in the sockets, and then you want to make blow the rinse water out with a blast of air from a tank (like a regulator cap) so it does not sit in there.
I haven't installed one on a blacktip yet, but it should work great through the plastic housing. The transmitter just plugs between the battery and motor and display is strapped to the outside. The smaller diameter will likely cause a single contact point with the tube in the center of the display, instead of sitting on the mounting feet, but it should not move around. Does the blacktip use the small Anderson battery connectors or the 75A? If small connectors, $715, if large $745
Blacktips are 30A connectors... it’s a tiny DPV
_R