sump oil

sump oil (uncountable)

1. Lubricating oil contained in the sump of an engine; the waste oil drained from the sump at the time of an oil change.
   • 1960 December, “New G.E. Line diesel loco maintenance depot at Stratford”, in Trains Illustrated, page 767:

     Dirty sump oil is pumped out along a waste oil pipe line to storage tanks by the boiler house, to be used as boiler fuel.

• “sump oil”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.
• “sump oil”, in Collins English Dictionary.