I used a salvaged motor for an old printer to creater a small submersible pump.

The design includes the housing, impellar and to be used with some flexible tubing. The outgoing OD is 10mm. 

The end cap is not a super snug fit, as I wanted to seal with sealent of hot glue, also where the cable enters. This ensures it is water tight. 

For the gasket I used an old inner tube, the thinnest I could find. Hot glue would probably work too.

Just be care when powering, as all printers have different tollerences. If the impellar or motor shaft rubs, it will pull higher current. I used a current limitor power supply when testing This way the cable and motor were safe.

The model in the image was printed with a 0.6 nozzle but a 0.4 will print fine. PETG was used.

M3 brass inserts were used to attached the housing to the impellar housing and countersunk M3 bolts.

I've included a link to what motor was used, although I'm no way associated with them. It is just the first link (https://www.ep-mediastore-ab.de/hp-motor-cm751-60154-oj-8100-8600-p-61970.html)

Build and use at your own risk with the submersible, as electricity and water can be dangerous.

Designed a smaller version using a 5V motor;

https://www.printables.com/model/695739-submersible-pump-using-5v-hobby-motor

EDIT;

Added the Fusion files, if you need to edit them.