How have people figured out bottle deposit returns?

[EdensTableFarm]

I am selling milk in glass bottles.  I pay a deposit for each bottle to the supplier and get a refund for the return.  I'd like to do a bottle deposit and return for my customers when they return the bottles.  I can't figure out how to do this in the Square POS.  

Has anyone figured this out?

[Lovewell]

@EdensTableFarm So what I would think is creating an item in your library for the deposit, and then when someone brings a bottle back you can do a discount for a set amount! I think that would be super simple!