27 C.F.R. § 19.202 Alternate use of premises and equipment for customs purposes.
Title 27 - Alcohol, Tobacco Products and Firearms
(a) General. The premises of a distilled spirits plant may, as provided in this section, be alternately curtailed and extended to permit the facilities of the distilled spirits plant to be used temporarily by customs officers, under applicable customs law and regulations, for the purpose of gauging or processing distilled spirits. The use of the excluded portion of the premises for customs purposes is subject to the approval of the district director of customs. When it is necessary to convey spirits in customs custody across the premises of a distilled spirits plant, the proprietor shall comply with the provisions of §19.99. When a portion of the distilled spirits plant premises is first to be excluded as provided in this section, the proprietor shall file with the appropriate TTB officer (1) an application for registration, Form 5110.41, to cover alternate curtailment and extension of premises, and (2) a special diagram, in duplicate, delineating the premises as they will exist, both during extension and curtailment, and clearly depicting all buildings, floors, rooms, areas, equipment and spirits lines (identified individually by letter or number) which are to be subject to alternation, in their relative operating sequence. Once such qualifying documents have been approved by the appropriate TTB officer, the designated premises and equipment may be alternately curtailed or extended pursuant to notice on Form 5110.34. Portions of the premises to be excluded by curtailment or included by extension shall not be used for purposes other than as set forth in the current notice. The proprietor shall remove all spirits from the premises or equipment affected by the notice prior to the effective date and hours of the notice. However, on release by customs, spirits being transferred to bonded premises under 26 U.S.C. 5232, may remain on the premises to be reincluded in bonded premises. (b) Separation of premises. The portion of the premises which is to be excluded from the distilled spirits plant premises as provided in this section shall be separated from the remaining portion of the distilled spirits plant premises in a manner which satisfies the appropriate TTB officer that the revenue will not be jeopardized. (c) Exception. Notwithstanding the provisions of paragraphs (a) and (b) of this section, the bonded premises may be used temporarily without filing Form 5110.41 or Form 5110.34, for the sole purpose of gauging bulk distilled spirits to effect their transfer from customs custody to TTB bond. (Sec. 201, Pub. L. 85–859, 72 Stat. 1349, as amended, 1358, as amended (26 U.S.C. 5172, 5178))
Title 27: Alcohol, Tobacco and Firearms
PART 19—DISTILLED SPIRITS PLANTS
Subpart G—Qualification of Distilled Spirits Plants
Alternate Operations
§ 19.202 Alternate use of premises and equipment for customs purposes.

