I think the pre-filter was stock on early vanagons.
The problem is if the pre-filter clogs the pump with cavitate.
This will damage the pump.
However, if the screen inside the gas tank clogs the pump will cavitate
anyway.
You can tell if the pump is starved for fuel by the change in tone.

Leave it in, take it out.. I dunno..

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Troy
Sent: Monday, February 20, 2012 4:05 PM
To: vanagon@GERRY.VANAGON.COM
Subject: gasoline prefilter

Hi folks:

I have an 89 vanagon westy. I have a square prefilter before the main
canister fuel pump, and I'm told this is not a stock set up. I have also
read in various posts how rust/sediment in the tank can get lodged in the
fuel pump, so wondering if I should just leave the square prefilter in place
when I replace my fuel pump. Is there any harm to doing this? It apparently
has been working fine for years this way.

Troy