You get credit for the tip-outs by subtracting them from the tips that you received before you report your tips to your employer. There is no way to deduct tip-outs on your tax return. When you report your tips to your employer, you are supposed to report only the amount you actually kept, after subtracting tip-outs. The amount you tipped out should not be included in your W-2. If your W-2 includes the full amount of tips that you received, before subtracting tip-outs, you should ask your employer to issue a corrected W-2 that does not include the amount you tipped out.
You should read IRS Publication 531 for all the details of how to report tips. You can download it from the following link on the IRS web site.
Publication 531, Reporting Tip Income