27 C.F.R. § 26.196
Under the provisions of this subpart and § 26.86 , distilled spirits brought into the United States from Puerto Rico in bulk containers may be withdrawn by the proprietor of a distilled spirits plant from customs custody and transferred in such bulk containers or by pipeline to the bonded premises of his plant, without payment of the internal revenue tax, if any, imposed on such spirits by 26 U.S.C. 7652 . Such spirits so withdrawn and transferred to a distilled spirits plant (a) may be redistilled or denatured only if of 185 degrees or more of proof; and (b) may be withdrawn from internal revenue bond for any purpose authorized by 26 U.S.C. chapter 51, in the same manner as domestic distilled spirits. Spirits transferred from customs custody to the bonded premises of a distilled spirits plant under the provisions of this subpart shall be received and stored thereat, and withdrawn or transferred therefrom, subject to applicable provisions of part 19 of this chapter. The person operating the bonded premises of the distilled spirits plant to which spirits are transferred under the provisions of this subpart shall become liable for the tax on distilled spirits withdrawn from customs custody under 26 U.S.C. 5232 , upon release of the spirits from customs custody and the person bringing the spirits into the United States shall thereupon be relieved of liability for the tax.
27 C.F.R. §26.196