You can pay back taxes in any way you like, but you will continue to get collection notices from the IRS unless you set up and follow an Installment Payment Agreement. Also, interest and penalties on the unpaid balance will continue to accrue.
Without an Installment Payment Agreement in place, the IRS may also take collection actions such as:
- Filing a Notice of Federal Tax Lien
- Serving a Notice of Levy, or
- Offsetting a refund to which you're entitled.
Here is the IRS Topic on Payment Options:
https://www.irs.gov/taxtopics/tc202.html
