There is no "Trust Fund".
The Social Security Trust Funds are the Old-Age and Survivors Insurance (OASI) and the Disability Insurance (DI) Trust Funds. These funds are accounts maintained by the Department of the Treasury. They serve two purposes: (1) they provide a mechanism for keeping track of all income to and disbursements from the trust funds, and (2) the assets of the funds provide automatic spending authority. To clarify the second point, no legislation is needed to spend a portion of trust fund assets on benefits or administrative costs (the Social Security Act limits expenditures to benefits and administrative costs).
Benefits to retired workers and their families, and to families of deceased workers, are paid from the OASI Trust Fund. Benefits to disabled workers and their families are paid from the DI Trust Fund.
A Board of Trustees oversees the financial operations of the trust funds. The Board reports annually to the Congress on the financial and actuarial status of the trust funds.
How about a Lock Box?/sarcasm