27 CFR 26.199a: a Action by revenue agent.

(a) Gauge. Puerto Rican spirits to be withdrawn for shipment to the United States as provided in this subpart shall be gauged by the revenue agent prior to withdrawal from the consignor premises. The revenue agent shall record the quantity and proof of the spirits gauged on TTB Form 5110.31. If the spirits are in packages, the revenue agent shall prepare in sextuplicate a package gauge record according to § 26.164a, attach the package gauge record to TTB Form 5110.31, and dispose of the form (and any attachments) according to the instructions thereon.

(b) Sealing bulk conveyances. When a shipment is made in a tank, van, or other bulk conveyance (other than barrels, drums, or similar packages that are not containerized), all openings affording access to the spirits shall be sealed by the Puerto Rican revenue agent is such manner as will prevent unauthorized removal of spirits without detection.