What is the percentage of backwash in a beverage?

Backwash is a slang term used in the beverage industry to refer to the leftover drink or liquid remaining in a cup or glass after it has been consumed. It is typically a small amount of liquid, but the percentage can vary depending on the size and type of beverage and the individual drinking it. In general, the percentage of backwash in a beverage is relatively small, usually less than 5% of the total volume of the beverage.