There are allways vacuum in 2 stroke engine each time piston are raising from crankcase to combustion camber, if not the engine can not take fuel though carburator...

I has allways the tube from crankcase to out in free and not to connect to tank (some engine has tupe from crankcase to intake manifold).. There are dirt of old oil out of crankcase after the oil has cleaned and lubricated engine + remove crankcase gas from combustion. Can not understand why you will connect to tank when you has pressure from exhaustmuffler or use perry fuelpump...

Jens Eirik