I'll have to disagree that the draft tube will not draw in air. Yes, the majority of the movement is out, but it does take in air also. Kind of one breath in, and two breaths out.
Yes, it was tied into the air intake to reburn the gasses, but it was also to filter out smaller particles of dust.
I still believe that a better filter is needed. If anything the draft tube should be lengthened. If you were to take some heater hose and route the draft tube back behind the cab (or further), that would help eleviate fumes and make it even more unlikely that dirt/dust would enter the crankcase.
