If a claimant who is eligible for benefits discloses an obligation to pay child support, the Secretary shall send notice of the eligibility to the child support enforcement unit that is enforcing the obligation. The Secretary shall deduct and withhold from any benefit payable to a claimant who is liable for child support the greater of: the amount specified by the claimant to be deducted and withheld to satisfy the child support obligation; the amount determined under an agreement submitted to the Secretary under § 454(19)(b)(i) of the Social Security Act; or any amount otherwise required to be deducted and withheld through legal process as defined in § 459(i)(5) of the Social Security Act. The Secretary shall: pay any amount deducted and withheld under subsection (b) of this section to the appropriate child support enforcement unit; and treat the amount as if it were paid to the claimant as benefits. The child support enforcement unit shall reimburse the Secretary for administrative costs incurred to carry out this section.