I couldn't wait to finish my last batch of corn starch. I did experiments to show that it's bad, just to finish the bag.
Potato starch is of very different chemistry. It cost about the same, ~$1 a 16 oz bag (?). You can find it in many Asian supermarkets along side corn starch.
It works if you microwave the solution, but for a uniform fleshlight, it's better to heat it in a small pot.
The mixture is 500 ml with 8 milk scoops. I think each scoop is 2 oz or 30 ml.
The potato starch is very good to work with. It doesn't give out dust when dry. It dissolves in cold water. It dissolves in warm water without forming gel prematurely.
If you heat the mixture gently and keep stirring, when it reach the right temperature, all of a sudden the whole pot forms a sticky semi-solid paste.
Pour it in a plastic cup and then insert in the middle a stick of your size.
The current mix ratio is probably too thick. The fleshlight didn't break, probably will hold up if you take it out of the plastic cup. Of course it's soft and doesn't hurt, but you don't move freely or you can't enlarge the hole easily. If you can enlarge the hole easily, the whole fleshlight will not stand up to any abuse.
So first you need a stick that fits you. Then I think you need lub. Or I'll experiment on two layers.
The good thing about potato starch is that it doesn't flow out and it's dry. So you can make a hole in the cup to avoid the vacuum pump effect and you don't need an outer cup to keep things neat and tidy. You can turn the cup upside down, pump away, and still no mess dripping down, until you cum.
I tried other flours, but you know what you are getting, like flour dole. They may have other uses but the base material have to be starch, potato starch.