Full Sewage Repipe - Tax Deduction or Add to Basis?

[Tracy M.]

Happy Friday, folks.  I own a 1972 duplex that's had ongoing plumbing back-ups.  The cast iron sewage pipes are done for and the only permanent fix is to replace the entire system with PVC.  Excavation adds a huge cost, so I've gotten multiple quotes that have all come out between $20k and $40k. 
I don't plan on selling any time soon, so I'm prepared to bite the bullet and get it done, and will probably finance the cost with the plumbing company to avoid spending cash.  

Questions:

1) Does something like this count as a "repair" (tax deductible) or "improvement" (which I believe adds to my cost basis, but isn't tax deductible)?

2) If repair:  The financing would be for three years.  Do I: 

     a. deduct the actual amount being financed the year that I do the repair (e.g. 2022) OR

     b. deduct the amount paid to the finance company (including principal & interest) each year over the three years?

3) If improvement: Do I:

     a. add the actual cost of the work to the cost basis the year that I do the repair (e.g. 2022) OR

     b. add the amount paid to the finance company (including principal & interest) each year over the three years?

Any input appreciated!  Thanks in advance!