I have seen plenty of places here charging a percentage rate for debit card use, as recently as last week. Not saying they should but it happens.
Who ends up benefiting from all the cash skimming I'm not sure, but chances are they are already filthy rich.
Get some denture tablets, unflavoured or a flavour you don't mind, put two in the camel back and fill it up. Let it sit for a day and rinse out. Repeat a few times if needed. Helps strip a lot of the residue manufacturing solvents out. It won't be perfect but it will be a lot better.