Why does my bus smell of exhaust fumes?

Like Zeds said big pipe, roughly as big as the end of your finger in diametre

 

They speak the truth. If the crankcase breather's not connected, all those oily fumes from the engine will be sucked straight into the heating arrangements.

It's a classic VW design "feature"

 

i had exhaust fumes in the van it turned out to be worn rear door seal have twin empi tail pipe it was being sucked in vortex style . new seal gone .