If your tank is higher than the ip, you prob can get away with not having an aux pump. I've had very poor luck getting veggie oil in a tank under the bus to flow into the injector pump without a pump.
while you're playing with fuel lines, you should put a pump, or at least a priming bulb on the diesel fuel line. This one is more important than the veggie line to me. when running veggie, you WILL run out of fuel from time to time. It can be a major project priming the stock fuel system once air is introduced into the system. The difference between a having a diesel pump and not having one are this.....
you're cruising along on veggie and the engine dies....you could be out of fuel, have plugged veggie filter, or any other veggie problem. if you have electric valve to switch between veggie/diesel, and you have a 12 volt electric pump on the diesel fuel line, you simple flip a couple of switches, turn the key and she'll fire right up while you're still rolling. Conversely, if you don't have a pump on the diesel side......you have to stop the bus, or if you don't have enough speed park in the middle of the street. Get out, open the hood, run around to the drivers side, stand between the tire and the frame rail, pump the little hand pump on the side of the injector pump approximately 15 thousand times, then run around and try to start the engine.....then come back and pump the little hand pump again, then run back and try to sthart the engine: repeat...
i have had very good luck with a middle of the road idea, which is one of these, available from wal-mart here in michigan. simple, effective, no wires, and moves way more fuel than the hand pump on the side of the injector pump. you can squeese the primer bulb till it gets kidn of hard, then pump the stock hand pump about 10 or 15 times, then start the engine, and pump the primer bulb a few more times till she starts running smoothly.