Let's imagine this situation https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTxrzyl_E9ig49eoN3MRO4EvmTI30cJ-BwTyA&usqp=CAU There is some hydrostatic pressure in the supply tank which causes the water to flow to the pump, which then pumps this water upwards. Due to some law of physics, I would assume that the pump cannot generate a flowrate higher than it's supply flowrate (it can't put out more water than comes in).
The water flow from the container is proportional to the height of the water. It drops as the tank empties.
Is it correct to say that the pump flowrate will also drop over time during this transfer? And you cannot affect this by increasing the pump RPM?