DIY menstrual cup
This is how to make a menstrual cup out of aquarium sealant for less than 5US$:
It is important to only use aquarium sealant. Aquaria silicone is the same as medical-grade silicone - aquarium sealant must be as pure as medical-grade silicone or else it might hurt the fish. Other kinds of silicone might have dangerous impurities or additives.
Note: I have yet to test this. It is only hosted on my site because I couldn't find the original link. When I get the chance to test it, I'll report back. If you decide to make cups, let me know how it goes!