A mini bike pump can be good at squirting, but some work is needed. You can’t easily fill a bike pump with water. Bike pumps use an O-ring seal or conical seal which moves and lets air in when you pull back. So when you put the pump into the water and pull back to fill, it does... nothing. You can fix this by substituting the O-ring with a fatter one, or by putting hot-melt glue inside the large end of a conical seal, thus sealing the piston in both directions. Axial outlet pumps work as they are, but it’s better to saw off the end of right-angle-ended pumps.
What about a Super Squirter, again a cylinder and piston, but made from polypropylene 40/32mm plastic plumbing pipe? Wrap tape over an elastic band to make a homemade ‘O-ring’ for the seal on the 32mm piston, and glue a champagne cork in the tip. The nozzle can be a hole in a piece of plastic retained by half...