Appears to be polyethylene to me.  I would think cross-linked rather than linear.  My guess would be Nalgene brand, which is often considered "best."  Maybe a screw thread with Teflon tape would work.  I'm no plumber, though.  Given how thin the tank wall is, would be iffy, I guess.  Consider though, that I'm no plumber, before you tap that tank.  David Mc

---- gneiss9 <gneiss9@GMAIL.COM> wrote: 
> I am trying to attach a PVC tap to my '91 Westy potable water tank  
> drain.  Does anyone know what material these Vanagon Tanks are made of?
> 
> So far the VW parts dept. that I've called in my area doesn't know  
> what kind of plastic the tanks are made of.
> 
> What kind of adhesives will work to attach PVC to the water tank  
> drain spout?
> 
> 
> Thanks,
> 
> Trevor Reynolds
> 
> gneiss9@gmail.com
>       
> Fahrvergnügen!