As gingerbob says, but I use carb cleaner as it seems to work better ( and yes the filter housings letting in air is a very common occurence on these vans), however if you want to try bypassing the filter altogether proceed as follows:
Yes you can run from a can to try it. Get yourself a hand fuel primer from a motor factors (should be less than £10) then remove the two left hand pipes. Use clear tube to the diesel can. Connect the primer to the tube from can to the front one of the two pipes, arrow facing towards the ford pipe. run a streight length of tube from the other pipe to the can. Ignore the two pipes still on the filter as these come from the tank. crack injector nuts loose, (19mm) then pump primer untill fuel escapes from around one or maybe two injectors, keep pumping until no more air bubbles come out, then tighten that injector / injectors. either very quickly blip the starter to shift engine but NOT start it, or use a 15mm socket on the very bottom crank pulley to rotate the engine about half a turn clockwise. Pump primer again and you should get fuel from another injector...nip this up, repeat until you have done all 4 injectors (takes about 2 mins to do...and about 40mins to try and explain it!!) after yu have bled all injectors, keep pumping primer until no air bubbles appear in the other clear tube going back to the can, then start the van. (be prepared for a little extra cranking / rough running to start with) immediately on getting it running properly, increase the revs to a fast idle (about half inch of pedal movement) and hold there for a least 2 minutes. After this allow the van to idle, inspect the clear return tube agian for signs of air bubbles (very very tiny ones are no real issue) If all is ok then the van should now run / rev as normal.