holding tank

plural holding tanks

1. A container for storage toilet waste in a vehicle
2. A holding cell

   1 more example

   After arriving at the Area A police station, I renewed my protests that as a working reporter with visible police credentials, I should not have been arrested. The desk sergeant insisted that I be booked, however, and I was put into the holding tank, a fifteen-by-fifteen dark and filthy cell, with 49 other people.

   1983 December 24, Larry Goldsmith, “Cops Bust 70 Anti-Nuke Demonstrators”, in Gay Community News, volume 11, number 23, page 6