AIM-2 in-line purifier (L 10" D 2") has 1/4" tube fittings welded in both ends (less change for leaks). Simply push your 1/4" tube into the fitting untill it can't go any further. Rated for 9,000 gallons.
Push 1/4" tube into input side of filter. Turn water on and flush for a while until the water runs clear (may come out black at first due to loose carbon fines). Turn water off and push 1/4" tube into output side of filter. Turn water on and check for leaks. To remove Tube. Hold down white colar around the tube fitting and pull tube out.