If you are unable to pay the tax debt in full, and an installment agreement is not an option, you may want to explore filing an OIC. An Offer-In-Compromise is an agreement between the taxpayer and the IRS that settles the taxpayer's tax liability for less than the full amount owed. The IRS will not accept an offer if they believe that the liability can be paid in full as a lump sum payment or through a payment agreement.
There is a $186 application fee, and depending on your abiity to pay within a 24 month time period, a 20 percent lump sum payment may be required or periodic payments to be paid while the OIC is being considered. Should the OIC be denied, rejected as not-processable, or withdrawn, these payments are not refundable as they are considered payments on tax.
If your offer is accepted, you must timely file all tax returns and timely pay all taxes for five years or until the offered amount is paid in full.