I installed a catch tank in place of the whole inadequate (IMHO) separator-flame trap assemble. I get a similar slimy, whitish stuff in the tank. I think it is oil foam. Smells like crankcase fumes. However, I've had no running problems. If it is clogging the line, it may be blocking the vacuum line to the manifold until it is sucked out or blown out by crankcase pressure. Try leaving the vacuum connection to the flame trap open.

You could have a leak down test done on the cooling system if you suspect a bad head gasket or a cracked head. Are you loosing coolant?