Sometimes tips are shared equally among the servers. If there are bussers the servers then tip out the bussers, usually 10-20% of the tip. Bartenders also get tipped out if they provide drinks for the servers. Kitchen gets naught.

I haven't yet been to a restaurant which has the audacity to add 20% to the bill for a tip. Some chinese restaurants which do dim sum automatically add 15-18% but I've yet to see 20%.

Remember, always tip on the pre-tax amount, not after tax. And don't forget to talk with the manager if service is not up to par.

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