Of my allocated tips, I tip-out 15% to the busboy and 5% to the bar. Where do I deduct this on my tax return?

You cannot deduct tip-outs (the tips you split with other employees) on your tax return. Nor can you deduct them from your allocated tips. The practice of tipping-out is one of the reasons you should keep a detailed daily log of your tips. If you document that you tip-out, and you reported all your tips to your employer, then you do not include in your income the allocated tips in box 8 of Form W-2.

Tipping-out, by itself, should not cause an allocated tip situation. First, when you report the cash tips you receive, you should report the total tips, then the amount tipped-out. Publication 1244 (PDF), Employee's Daily Record of Tips and Report to Employer, includes Forms 4070 and 4070A, Employee's Report of Tips to Employer that provides the following lines:

The detail of the information provided should enable your employer to develop a reasonable, fair, and accurate method for determining whether tips need to be allocated, and, if so, how much. Employers who operate large food and beverage establishments are only required to allocate tips if the total tips reported by all the employees who customarily receive tips are less than 8% of gross sales. Thus, when there is a tip-splitting arrangement, it is important that all tips, including those received through tip-splitting, be reported to the employer by each employee who receives $20 or more in a month.

For more information, refer to Publication 531, Reporting Tip Income.

As an employer, do I have any liability if my employees receive tips but don't report them to me?

Employees who customarily receive tips are required to report their cash tips to their employers at least monthly, if they receive $20 or more in the month. Cash tips are tips received directly in cash or by check, and charged tips. You have a liability to withhold and pay Social Security and Medicare tax on your employees' reported tips, to the extent that wages or other employee funds are available. If the employee does not report tips to you, it places you at risk of possible assessment of the employer's share of the Social Security and Medicare taxes on the unreported tips. If you are a large food or beverage establishment (more than 10 employees on a typical day and food or beverages consumed on the premises), you are required to allocate tips if the total tips reported to you are less than 8% of gross sales. Report the allocated amount on the employee's W-2 at the end of the year.

If the reported tips from employees are more than 8% of sales, must an employer still allocate tips to the employees?

No. Tip allocation is required when the amount of tips reported by employees of a large food or beverage establishment is less than 8% (or an approved lower rate) of the gross receipts, other than nonallocable receipts, for the given period. If the employees are reporting more than the 8%, there would be no allocated tip amount. However, the employer must still file Form 8027 (PDF), Employer's Annual Information Return of Tip Income and Allocated Tips.