Example. On February 1, 1968, an assessment is made and a tax lien arises with respect to A's delinquent tax liability. On February 25, 1968, in accordance with § 301.6323(f)-1 , a notice of lien is properly filed. On March 1, 1968, A negotiates a loan from B, the security for which is a second mortgage on property owned by A. The first mortgage on the property is held by C and has priority over the tax lien. Upon default by A, C begins proceedings to foreclose upon the first mortgage. On September 1, 1968, B pays the amount of principal and interest in default to C in order to protect the second mortgage against the pending foreclosure of C's senior mortgage. Under local law, B is subrogated to C's rights to the extent of the payment to C. Therefore, the tax lien is invalid against B to the extent he became subrogated to C's rights even though the tax lien is valid against B's second mortgage on the property.
26 C.F.R. §301.6323(i)-1