Well, I'll take a pollen problem vs. a giardia problem.  I'm gonna try the back-flush thing though and see how that work out.  After each trip I soak the filter in bleach and then run a 1/2 bag of water through it to flush.  Since I will probably be getting a new filter for next year it's worth a shot I suppose.  Too bad they dont make the filter with removable parts and simply replace the charcoal and cloth filter as prn - like my pool filter.