I was soaking my XL Rocket Stem in some tupperware, but that's a waste of isopropanol. This handy container with cap will let you store your rocket stem and also soak it in a minimal amount of alcohol. 

Printing is super simple, no supports needed. You may want to use a more heat resistive material if you want to store your stem right after use. I just used PLA+.

Use is easy too, I recommend putting the stem in first and then if soaking pour in the ISO after and throw the cap on. When removing the stem take it to a sink because it's likely to pick the liquid with it as you lift it out.