D.C. Mun. Regs. tit. 9, r. 9-3704
The values used in determining the tax shall be used for purposes of making the apportionment required by § 15 of the Act.
Any exemption or reduction allowed by reason of the relationship of any person to the decedent or by reason of the purposes of the gift shall inure to the benefit of the person bearing that relationship or receiving the gift.
The following credits shall inure to the proportionate benefit of all persons liable to apportionment:
To the extent that a gift or bequest does not qualify for a full marital or charitable deduction for purposes of the federal estate tax solely by reason of an inheritance or estate tax or other death tax imposed upon and deductible from the gifted or bequeathed property, the property shall not be included in the computation provided for the D.C. Code § 47-3714, and to that extent no apportionment shall be made against the property. This exception shall not apply in any instance where the result will be to deprive the estate of a deduction otherwise allowable under § 2053(d) of the Internal Revenue Code of 1986, relating to the deduction for state death taxes on transfers for public, charitable or religious uses.
In all cases in which any property required to be included in the gross estate does not come into the possession of the fiduciary or other person required to pay the District estate tax or the federal estate tax, he or she shall be entitled, and it shall be his or her duty, to recover from whomsoever is in possession, or from the persons interested in the estate, the proportionate amount of the taxes owed under the provisions of the Act.
If the fiduciary or other person required to pay the tax cannot collect from any person interested in the estate the amount of the tax apportioned to the person, the amount not recoverable shall be equitably apportioned among the persons interested in the estate who are subject to apportionment.
If the fiduciary or other person required to pay the tax transfers any property included in the estate to another person, other than a bona fide purchaser for value, the transferee shall be jointly and severally liable with the transferor for the amount of tax apportioned to the transferor under this section, less the value at the time of the transfer of any consideration furnished by the transferee for the property.
None of the provisions of the Act shall in any way impair the right or power of any person by will or by written instrument executed inter vivos to make direction for the payment of taxes and to designate the fund or funds or property out of which the payment shall be made; and in every such case the provisions of the will or of such written instrument executed inter vivos shall be given effect to the same extent as if the Act had not been enacted.
D.C. Mun. Regs. tit. 9, r. 9-3704