"Java Jive" lyrics

The song “Java Jive” is all about drinking coffee and tea. One of the verses is"

*Oh, slip me a slug from the wonderful mug
And I cut a rug till I’m snug in a jug
A slice of onion and a raw one, draw one.
Waiter, waiter, percolator!

*What is the meaning of the third line? Do some people have a slice of onion with their java?

I always thought “raw one” was old fashioned lunch-counter talk for a hamburger. I know “draw one!” was for a cuppa.

It’s heaven on Earth with an onion slice.