I dun suggest u use water to wash yr CPL! Water will get in between the CPL and gets trapped there. Usually the rear exposed part of the part where polarising works and cleaning that part will damage the coating.
does the filter when look under the light appear like uniformly jit-liap jit-liap debris stuck onto the glass?
Yes, it look like this. If just look at without directing to the light, it is very clear. But it looks dirty if directing it to the light. I will not washing it and that dirty seems caused by the process of manufacturing.
It is brand new which is bought from tcw. It is cheapest one i found so far. 67mm hoya CPL cost 50SD. I am just wondering whether all the hoya CPL looks like that. If you donnot direct the cpl to the light, it looks very clear. maybe , you can try to look at it by directing it to light.