the water spray exiting the tube is much more nice and linear at higher speeds, but then the flowrate is much too fast. Maybe using a much smaller rubber tube would help with that (wikipedia's page on these types of pumps says "The flow is pulsed, particularly at low rotational speeds" which isn't exactly good for 3d printers)

They could also lasercut this design at the same time they are lasercutting the rest of the printer, since it's made of 2d shapes.