Watts PremierWP560060 RO Water Filtration PH Balancing Ceramic Filter with 1/4 inch QC Fitting, 11 1/2 Inch, Multi

which one is the input and output?

How should this filter be mounted: vertically or horizontally?

Do I need to flow some water through it after installing like carbon filters require?

The Watts RO-Pure has 1 line to/fro the tank. Water flows thru the post filter as it comes back from tank to faucet. Where does ph filter go? thx