In the administration of any trust which is a “private foundation” as defined in § 509 of the internal revenue code of 1954, or which is a “charitable trust” as defined in § 4947 (a) (1) of the internal revenue code of 1954, there shall be distributed, for the purposes specified in the trust instrument, for each taxable year, amounts at least sufficient to avoid liability for the tax imposed by § 4942 (a) of the internal revenue code of 1954.