EGGBUG is the Splatoon 3 Pool code for Cohost! Joining it offers little benefit beyond occasionally seeing usernames you recognise in the lobby and the theoretical ability to join games with people (which I've never managed to do), but if you're not in another Pool, I can suggest joining it just to make things seem a bit more lively.
At time of posting: I'll probably be there for the first timeslot of the upcoming "duos" Challenge, should anybody want to be helped hindered by me for that.