PLEASE READ THE ASSEMBLY AND PRINTING INSTRUCTIONS BELOW
This was just a quick shot at an external gear pump, I wondered if it was actually possible to make a working water pump. It works, doesn't leak, and I'm actually really happy with the result.
0.2mm layers, 50% infill, no support (designed with 3D printing in mind)
Print the gasket with the most flexible material, if not available, seal it any other way. Use the file gear, if your printer isn't capable of good tolerances, use the file gear_tight if it is (any machine above $300 should be able to do that). There are two housings to choose from, the _mount file has two mounting holes, whereas the regular one is just a unit.
You can watch the tutorial bove, however I do reccomend you to read the written version as well.
To assemble this pump, you'll ned a couple more things: a 2mm shaft, rubber band, an electric motor or whatever to power it with (has to have a 2mm shaft, might have to do some coupling) and some grease. Print out every part according to aforementioned settings. Take a 2mm drill and drill one of the gears. Then take a 2.2mm drill and drill out the other one. The gear with a bigger hole will be the idler gear. Then take the shaft and cut 15mm off of it. That will be the idler shaft. Next up, it press fit the drive gear onto your drive shaft so that about 2mm of the shaft is protruding. Insert both gears into the housing. Now, take some grease and put a dab of it into the cutout on the drive shaft hole. Using a piece of a rubber band, seal the drive shaft. Take the printed gasket and put it in place. Cover it with the remaining part and screw it together using either M3 screws and a nut, or in my case, use an M3 threaded rod and a nut on each side. That's it, now just hook up your hose and you're good to go. Hose opening is 6mm in diameter.