Grant

You've used up the acid. Add more (no need to decant, it's liquid after
all so it will diffuse) and it should eat the metal again. It will
probably take 5 - 10 ml of 70% HNO3 to eat a small screw. When you get
to taking out the screw from the aluminum, build a dam around the hole
with modeling clay and then rise the acid off with a baking soda rinse
when you're done. Just rinse it down the drain, the beasties at the
treatment plant like nitrates.

By the way, general rule in chem labs is rinse and dump 3 times.

Jim