IRS Installment Agreement
For more info on these, you can read here. In order to apply fill out IRS Form 9465, Installment Agreement Request. They will want the balance paid off in 3 years max. You will owe penalties and interest.

IRS Partial Payment Installment Agreement
Similar to a regular Installment Agreement (above) except the payments do not pay off the tax debt in full. After the terms of the Installment Agreement are fulfilled, the remainder of the IRS Tax Debt is forgiven. Although requesting a Partial Payment Installment Agreement with the IRS is easier than submitting an Offer in Compromise, it’s still tricky. First, you need to write a letter stating your request for a Partial Payment Installment Agreement and submit it to the IRS along with IRS Form 9465 and IRS Form 433-A.

Borrowing from a bank or credit card
If you have the option of borrowing from a bank to pay off your tax debt, this will give you the best rates. Penalties and Interest assessed by the IRS on Tax Debts are a lot higher than a typical loan from the bank. A typical Bank Loan, if you can get one, is around 6.5% interest versus Penalties and Interest on an IRS Debt which is usually 8% compounded daily. A Credit card will most likely have a much higher rate and should be seen as a much later option.

Offers in Compromise
Read more here about this possible but unlikely solution to settle with the IRS on a lower amount.

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