27 C.F.R. § 70.506
Claims to which this subpart is applicable must be executed on Form 2635 (5620.8) in accordance with the instructions on the form. (For provisions relating to handcarried documents, see 27 CFR 70.304 ). Claims for credit or refund of taxes collected by district directors of customs, to which the provisions of section 6423, I.R.C., are applicable and which Customs regulations ( 19 CFR Part 24 -Customs Financial and Accounting Procedure) require to be filed with the appropriate TTB officer, must be executed and filed in accordance with applicable Customs regulations and this subpart. The claim must set forth each ground upon which the claim is made in sufficient detail to apprise the appropriate TTB officer of the exact basis therefor. Allegations pertaining to the bearing of the ultimate burden relate to additional conditions which must be established for a claim to be allowed and are not in themselves legal grounds for allowance of a claim. There shall also be attached to the form and made part of the claim the supporting data required by § 70.507 . All evidence relied upon in support of such claim shall be clearly set forth and submitted with the claim.
27 C.F.R. §70.506