It’s actually a drain spigot that you can hook up to some of the oil filter housings. Not needed on the Gen3 Prius (at least the ones I have looked at), but on our 2017 Lexus RX450h the oil filter housing is designed to have a central drain removed and the plastic spigot installed. I tried it and it didn’t work so well, as there still was oil In The housing upon removal . It came with your oil filter purchase?
Those are used for those A3 cartridge filters for Toyota and Lexus vehicle’s. The Prius uses an A1 cartridge filter, so they don’t use that. Honestly, that piece is the most useless piece ever, not worth your time doing it that way. Just my opinion.
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F252671558621 I'm confused as to why