The question here I think is: should implied_sex mean NOT to use the sex tag?
If it coexists then I guess the way you would exclude implied sex to only look at explicit sex would be to search sex and -implied_sex via tag-exclusion.
Probably also a good way to do searches for potential images that need the implied_sex tag since in a lot of cases people don't realize it's only implied (no visible dick-in-hole)
It also seems like there are DEGREES of implication but I wouldn't really know how to measure them.
IE you have "they shut off the lights and there's giggling" or "she's making an expression like there's a dick in her but you can't see below the belly" or "their crotches are smushed together with no clothes on"