Some of the liquid nitrogen dewar Try-Cock exhaust-to-atmosphere tubes were blocked or, partially blocked, with mud dauber wasp nests (a.k.a "mud') -> So, today I cleaned out each one via opening the Try-Cock valve and then feeding a wire up through the exhaust tube so as to dislodge the obstruction.  Once dislodged, the ~10 psig GN2 vapor blew the debris out onto the ground.  .