The tag implication #67715 3_sheaths -> multi_sheath is pending approval.

Piggybacking off of topic #57259, which would implicate 2_sheaths to multi_sheath

3_sheaths is a variant that is most commonly present on posts featuring cerberus or hellhound characters (3 heads, so 3 cocks - it tracks): https://e621.net/posts?tags=3_sheaths

This is treading the fine line where a tag may be too specific, but I think 3 is a good general cut-off point here due to the aforementioned association with cerberus/hellhound characters and any more becoming difficult to count due to being obscured by dick: https://e621.net/posts?tags=3_penises+%7Ecerberus+%7Ehellhound