As the IRS details on its website, the role of the Solo 401k plan trustee is a serious responsibility. All Solo 401k plan assets must be held in a trust, and a plan trustee must be named. The trustee holds plan assets and is usually responsible for managing the plan’s investments, although, if elected in writing, these functions can be delineated to the direction of another fiduciary, an investment manager, or Solo 401k provider. See ERISA 403(a), 29 U.S.C 1103
The Solo 401k plan trustee is responsible for processing contributions and investment transactions, processing disbursements, ensuring taxes are paid in the event of distributions and paying fees and expenses of the trust.