Brian, using a Reverso gear pump or similar, the system can be plumbed to be self filling. DC pump, so it will run in either direction, needing only a DPDT switch wired for polarity reversal, like a flap switch.
Most smoke systems have a solenoid valve at the firewall wired in parallel with the pump. It's open with the pump on, and closed when the pump off, for a nice crisp on-off supply to the hot exhaust.
Given this collection of parts, the system can be made self-filling by adding a tee-fitting at the pump outlet, connecting the extra leg to a belly quick-connect, and wiring the solenoid valve so it does not open when the pump switch is in the reverse direction. Just couple a siphon hose to the quick-connect, shove the other end into the oil drum, flip the switch, and monitor the smoke tank for quantity.