I have a Pentair Clean and Clear 420 filter. I'm trying to clear my pool of a build up of fine silt, and this is just blowing through the filter as I vacuum from the pool. In the parts diagram, there is a part called the lower manifold, ie part number 8. It has a pvc pipe rising vertically to the top of the filter assembly, and it has a cap of some kind at the top. The cap has deteriorated and is broken. I'm not sure exactly how the filter works, but I suspect this may be where I'm getting some bypass of the filters. I may also need to replace the filters, but I want to look into this broken cap first.
Can anyone explain the purpose of this vertical pipe and the cap at the top?