sump tank

sump tank (plural sump tanks)

1. A tank containing the liquid removed by a drainage system.
   • December 15 2022, Samanth Subramanian, “Dismantling Sellafield: the epic task of shutting down a nuclear site”, in The Guardian‎^[1]:

     The year before the pandemic, a sump tank attached to a waste pond sprang a leak and had to be grouted shut.