Help..Diesel MB. high school, metal shop project car

[oregonbarn]

I have been reading from this form for a bit now and the knowledge base seems to be unlimited about the diesel MB. I teach at a high school, metal shop, but we do lots of other areas including a veggie conversion on an 83 300SD. We made the tank, installed the heated filter and ran the hot water and veggie lines to the trunk. For the last 3 days we have been trying to get the air out of the diesel system so we can start the engine and finish the conversion. I have been pumping with the hand pump and it seems that air is getting into the system around the diesel filter. We have used fuel injector type hose clamps and a new filter, but after pumping for minutes the diesel just will not get the air out and when you stop pumping the fuel will retreat back toward the tank. We have the clear pvc lines and can see the flow. Any ideas or suggestions will be greatly appreciated.