Federal law allows a restaurant to force its servers to relinquish their tips, including to management itself. The restaurant just has to pay its servers the full minimum wage, rather than the lower service wage.

You probably leave about 20 percent. Maybe less if the service was slow. Maybe more if you received extraordinary service—or if you used to work in a restaurant. Whatever tip you leave, though, you probably expect that the tip actually goes to the person who served you.