Definition - What does Pit Pump mean?
A pit pump is a submersible pump used in reclaiming drilling fluid. The pit pump is located in the drilling fluid recovery unit. Because it's higher than the pit's bottom, it circulates the drilling fluid that's returning from the bore without picking up the solids returning to the reclaimer from the bore, which settle out of the drilling fluid.
Trenchlesspedia explains Pit Pump
A pit pump is part of the drilling fluid reclamation system, not part of the rig's mud (drilling fluid) distribution system. The mud pump is the heart of the mud distribution system, pushing drilling fluid down the drill string and back out of the bore. The mud pump is essential to the drilling operation. The pit pump is not, because the rig's shakers can remove solids from the mud before it returns to the mud pit to be pumped down the drill string again.