Its crazy but I have been dealing with a rusty tank for a year now on a
daily driver.
I installed a Fram filter 3/ 8 clear cartridge type from Wall mart   $3.50
in front of the pump.
I have gone through probably five of theses filters in the year . I have
continually had to pinch off the line w/ a vise grip and pull the filter loose
and knock out the rust so I get another couple tank fulls and than every  now
and than I splurge and put a new filter on.
The pump always gets loud and lets me know when it's time to clean the
filter.
I have not had to replace the original VW filter yet.
I started out with one of those glass hot rod filters with the changeable
element but they clogged very quickly and did not filter small enough particle
size so at one point the pump locked up on me (eight hundred miles from  home)
  I was able to pull the power and ground loose and switch them  to reverse
the pump and it restarted and flushed the rust back out the inlet .I  put it
back together normal and it has been going strong for another 10 k aside  from
still having to clean the filter every now and then.
One of these days I might actually replace that tank!   Probably  when a
cheap one finds its way to laying at  my feet.

Anyway,  I highly recommend running a pre-pump  filter to  everyone.

Jeff E
87' Westy "weekender"
Atlanta, GA.