Those are to give headspace so the gasoline in the tank will have room to 
expand.  Bentley has a reasonable drawing of the whole setup.

david

At 07:25 PM 4/2/2001, Javier wrote:
>Today I was looking under my Westy�s front wheel and saw, on both sidesof 
>the van a couple of plastic tanks that seems to contain gasoline coming 
>back from the tank?
>What are these for?
>
>All info will be highly appreciated.
>
>Javier Zavala
>84 German Westy
>01 Prospector Hovercraft

David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"