I use both a PurFlow inline filter under the sink, and an external inline filter at the pedestal. When it's time to winterize, the under-sink filter gets discarded and the plastic tube is installed before pumping in the antifreeze. Next spring, a new PurFlow filter replaces the plastic tube. IMHO, the second filter on the kitchen sink line should catch anything the outside filter misses. Never have any signs of mold or bacteria on either filter.
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.