https://www.law.cornell.edu/cfr/text/26/1.263(a)-1
§ 1.263(a)-1 Capital expenditures; in general.
(a) General rule for capital expenditures. Except as provided in chapter 1 of the Internal Revenue Code, no deduction is allowed for -
(1) Any amount paid for new buildings or for permanent improvements or betterments made to increase the value of any property or estate; or
(2) Any amount paid in restoring property or in making good the exhaustion thereof for which an allowance is or has been made.
把septic tank变成sewage肯定是betterment.
