Currently, erection_under_clothes implies erection, and erection implies penis which means we have pages and pages of posts where a penis is not visible but it is impossible to remove the penis tag.

erection_under_clothes -penis should show hundreds of results. Right now, it shows none. Additionally, now, there are hundreds of posts tagged penis -rating:e which is another symptom of the issue.

I'm not sure when this change was made, but it definitely needs to be reverted.

Same should probably apply to unwanted_erection. It implies erection which also implies penis, but an unwanted erection isn't necessarily always visible, it could easily be a stiffy still covered by clothing.