There's seemingly no male equivalent to the "all_three_filled" tag, so I was wondering if there was a specific reason for that? If not, "all_three_used" would work- it could even be universal.

If I understand correctly, this tag would be for a character's mouth + penis + anus all being used for sex at the same time (obviously this requires at least a threesome, if not a foursome). I don't think it's a bad idea, but it would get confusing with how it works with herms/maleherms, since they have four relevant types of parts (mouth, penis, pussy, anus).