Disclaimer : This is a copy of a medical device. This design has no commercial purpose and is for personal use only.

This famous, simple and effective device is made for nasal cleansing with saline water. (search internet for instructions)

you need to print it with a non-toxic material and make it waterproof

There is two files with 2mm and 3mm walls 

Printing tips : To make it waterproof, you can print it 100% infill with a high temperature for good layer melting. There is a bit of overhang on the small end and on the inside bridging but it's not a problem for a good printer.

For using on children you can scale it down by 20% to fit a child nose.

Here is a link to the measuring spoon (for salt) design already made by Stark :
https://www.printables.com/fr/model/119035-rhino-horn-odmerka-nacl