I need to know how to add a new tax liability in quickbooks so that it automatically deducts it during payroll processing.

Hello there, @zoesophiebookkee.

To give you the right amount of information, I'd like to ask if what tax liability you're referring to? 

If you're referring to unemployment or local taxes, QuickBooks automatically update the taxes as long as you've set up the address for local taxes correctly.

If you're referring to the withholdings, make sure to check your employee's allowances, status and your employee's details.

However, if you're referring to something else aside from the above mentioned, feel free to add your comment below. Have a good day!