There is a ball in the tube that allows gas to flow past it when you fill the tank but floats up and blocks gas from exiting back out the tube when you take a left turn.

Bryan

From: Scott Daniel - Turbovans 
Sent: Sunday, May 20, 2012 6:10 PM
To: Bryan Feddish 
Cc: vanagon@GERRY.VANAGON.COM 
Subject: Re: Fuel Filler Tube Question about BD part

I just changed one of those the other day ..
a used one ..
no 'floaty balls' anywhere that I am aware of.

what is this 'floaty ball' talk anyway ? 

On 5/20/2012 12:59 PM, Bryan Feddish wrote: 
Does anyone know if this tube: http://busdepot.com/details.jsp?partnumber=251201121D has that floaty ball in it?

Thanks,
Bryan