Figure out which guns you own are compatible with sewer water, in any form. I have one, a Cooey Arms, Winchester badged single shot with a birch stock. Maybe all of your guns are compatible with sewer water, maybe none.Put the guns you own that are compatible with sewer water in the soiled cases.
Then, throw the rest of the cases away. It will be cheap compared to having a decent gun refinished.
Maybe your shooting student has a bunch of guns that are compatible with sewer water, and you could sell them to him. Cheap.
You need better storage for your gun cases, by the way.


Best,
Ted