Oh yeah, the forces we're talking about here can really add up.. 14lbs/sq.inch or so. Not much on it's own, but square inches have a way of adding up!

So, whatever pump you get, the way to use it safely is probably to just make a small but sturdy plywood box to completely enclose your (open) jar of mixed up gel. A hole or two for airflow in the box is needed, then wrap the whole thing in plastic, duct tape it shut, with the pump hose passing through the plastic into the box at some location. pump.

Cheers