Hey, thanks for your interest! I edited the post to add an 'exploded' view of the parts. This is prototype #2 and still has some significant issues that I'm working on (and would love community input on!)

My strategy for a watertight print is as follows:

• lots of perimeters and solid layers top/bottom on the individual parts
• sand mating surfaces smooth and add TPU grommet/seal
• apply significant pressure to compress the TPU to form a seal

This has actually worked extremely well. The pump has leaks but none of them are from the 3d prints or mating surfaces. What I'm struggling with is preventing water from going out the shaft tunnel. This is a major issue because I'm currently using a chrome-steel bearing at the top for shaft concentricity, which will rust out almost instantly. I made the challenge harder for myself by using a hexagonal drive shaft so I can't rely on tight tolerances there to keep out the water. I need to sort out a strategy for packing / sealing and/or switch drive shafts + use some kind of off-the-shelf option.

I've also been looking into an alternate bearing solution e.g. ceramic. If I can find a good sealed bearing that won't rust I might be able to just use a tight TPU seal between hex shaft and bearing ID to give it a watertight seal.

The original design had several chrome steel bearings in it (newbie mistake) which I had to replace at the last minute with the nylon bushings. I'm working on a better solution.

edit: see video I just added in the post as well