D.C. Code § 47-2204
Every vendor or retailer not engaging in business in the District who makes sales at retail as defined in this chapter, and who upon application to the Mayor has been expressly authorized to pay the tax imposed by this chapter, shall, at the time of making such sales, collect the reimbursement of the tax from the purchaser and give to the purchaser a receipt therefor in such form as prescribed by the Mayor. For the purpose of uniformity of tax collection by the vendor or retailer who has been expressly authorized to pay the tax under the provisions of this section and for other purposes, the provisions of §§ 47-2003, 47-2004, 47-2009, and 47-2010 are hereby incorporated in and made applicable to this chapter. A permit shall be issued to such vendor or retailer, without charge, to pay the tax and collect reimbursement thereof as provided herein. Such permit may be revoked at any time by the Mayor who shall thereupon give notice thereof to the vendor or retailer.
D.C. Code § 47-2204