Is the fee for hooking up to city sewer considered a tax?

Answer 1

No, it is a fee, not a tax.

If you are looking at this as a tax deduction, it is only deductible as part of the cost basis for land and building you own or are buying, or 2) as part of a business expense if you are having to pay the fee and do not own the property.

Answer 2

No, it's a fee for a service, even if the local municipality calls it a tax.