D.C. Mun. Regs. tit. 9, r. 9-3706
Each application for an extension of time shall be in writing and shall clearly state the reasons for the request.
If an extension of time to file the estate tax return has not been obtained or, in the case of an extension, if the return or an additional extension is not filed within the extended time period, the penalty for late filing shall be assessed.
If an extension of time to pay the estate tax has not been obtained or, in the case of an extension, if the payment is not made or an additional extension is not filed within the extended time period, the penalty for late payment shall be assessed.
Any outstanding tax due remaining after the expiration of the due date for payment or of an extension of time to pay shall be deemed delinquent and shall be subject to penalty and interest under the provisions of D.C. Code § 47 -453.
D.C. Mun. Regs. tit. 9, r. 9-3706