^exactly, you can see all the APAP that you are getting out of it, its sitting there on the filter. If you have a clear solution then there is very little if any APAP in it. As long as you are getting out say 80% like you said, then a 10/500 only leaves 100 mg of APAP you are taking per 10 mg. And I think that is really low ball estimate @80% of how much APAP is coming out in a CWE. Yet again, if the solution is clear then you don't have much APAP in it, you will see it in the solution, it is not soluble in water, hence why it works.
My only issue with CWE is not knowing how much hydro/oxy I am not getting in the end.