I wipe a Q-Tip in a dilute solution of Zippo lighter fluid and Imperial Sizing Wax. The Q-Tip gets wiped around inside the case mouth about ⅛" deep.
It make case expansion easier and I get very little brass adhering to the nose of the expander die. It was the brass rubbing off onto the nose of the expander plug that got me lubing the inside of the cases.
The lighter fluid evaporates fast leaving a very thin coating of sizing wax behind.

I rub straight undiluted Imperial Sizing Wax onto my lube pad and roll my revolver cases on the wax prior to sizing them. The Imperial Wax wipes off easily with a micro-fibre towel. I found I could get a thinner coat of wax onto the outside of the case by rolling on the wax coated pad.