Outer Limits 4x4 Board

My cruiser (105 diesel) won't go, engine won't run. I can't get fuel to the filter. I use a CAV filter. with an adaptor. I try to prime it (pump and pump and pump), but no fuel flows. There is fuel in both tanks. Can't see any air or fuel leaks, haven't found any yet. Is it possible to have a fuel block? I tried switching between main and sub tanks, but it made no difference. Still could not pump fuel through.

Anyone else had this problem? Does it sound like a bad fuel blockage (I use real nasty fuel at times). Or does it sound like a problem with tank changeover solenoids? I can hear the solenoids clicking when I switch tanks, so I assume they work OK.
Cheers
Dave

well, for all the restless hordes out there wanting to know how I am getting on, I fixed it! The mighty cruiser runs again.

I thought the fuel line might be blocked with sludge or gunk, so I heated the line between the filter and the main tank with a heat gun. When I had it all nice and hot, I started pumping on the filter priming pump and lo and behold, out came some gooey stuff that you would never want to put near an engine. Spent the next hour recharging the battery (I killed it trying to pump fuel through) and draining the tank. Is all good now.
Cheers
Dave