D.C. Mun. Regs. tit. 9, r. 9-902
Each carrier shall keep accurate and complete records of the following:
On or before the last business day of each month, each carrier shall file a motor fuel report on the activities of the previous month on forms to be furnished by the Deputy Chief Financial Officer.
If the report shows an amount owed to the District after taking a credit pursuant to § 903, the carrier shall pay the amount of tax due at the time the report is filed.
If the final date falls on a Saturday, Sunday, or legal holiday in the District, the next business day shall be the final date for filing of the report and for paying any tax due.
Each report and payment of tax shall be considered filed and paid on time if mailed postage prepaid in an envelope properly addressed to the Deputy Chief Financial Officer that is postmarked by the Post Office Department before midnight of the final filing date.
The Deputy Chief Financial Officer may enter into agreements with appropriate authorities in states party to the compact for the cooperative audit of carriers' reports filed under the act.
D.C. Mun. Regs. tit. 9, r. 9-902