After you’ve complete the priming section on How to Assemble Video, stop and take each filter one at a time, place it under an over hang kitchen tap or outside tap, with the rod directly under the flow of the tap water.   Turn the water on slow and keep increasing until you have water flowing fast but not bouncing off the filter rod.  Leave it there for at least 10 to 15 minutes each, this is just an initial extra prime and will avoid future problems with water flow speed.  It will totally saturate the filters and so you should never need to do extra priming again, unless you allow the filters to dry out.  Give your Black filters, an occasional prime when cleaning, although priming well initially, will set them up to work fast long term.