I have 12 ibc totes connected via 2 inch PVC coming straight out of the bottom valve of each tote. The totes are arranged in 2 rows of 6 with each tote connecting to the PVC with tees. At the front of the rows, the 2 inch lines come together with another tee, and step up to 3 inch for the pump inlet (which I know is very much not ideal, but it works fine and all of this stuff is mounted on a trailer that's used for transporting water, so space is a major constraint.

The tanks also fill from this piping system with a connection to a fire hydrant, and the totes themselves have 2 inch connections on the front of them, so upgrading to a larger pipe isn't really useful for much other than mitigating slight friction losses. The top opening is currently unused but will eventually be plumbed for overhead filling. The system honestly works better than I expected it would, considering I designed the whole thing myself and haven't seen anything like it anywhere else. I'm just trying to refine the design.

The issue is, that when the tanks closest to the pump inevitably empty out first, the pump starts sucking air until I manually close the the valves on each side. What can I do to prevent or limit the pump pulling air from the nearly (but far from actually) empty totes? I have considered using 45s to angle the pipe that connects the totes together either up or down in relation to the valve, or maybe adding a u bend to the pipe after the last tote and before the pump. The pump is a 3 inch inlet harbor freight water pump. The pump is sitting nearly level with the bottom of the tanks, so when they are full, the pump is below the water line. When they are empty, the pump is above the water line.

What can I do to solve this? Thanks in advance.