noun
vat
VAT/væt/
A large tank for holding or processing liquids.
The large vat holds amber liquid above its bottom drain valve.

Etymology
Old English fæt meant a container. English vat came to denote a large tub or cistern, especially one holding liquor while it matured—a particular use closely matching today's liquid-processing vessel.
In context
you may have seen boc um and if you go to a hospital you'll see a great big white vat sometimes it will have oxygen in it