Game is very passive and hero has been raising a lot in multiway pots preflop but has insofar checked and folded almost all flops.

UTG is villain and is very loose and very passive.

BB, UTG, and UTG1 are the table fish, all loose/passive.

Preflop: Hero is MP1 with Q Q
UTG calls, UTG1 calls, UTG2 calls, Hero raises, 1 fold, MP3 calls, 3 folds, BB calls.

Flop: (11 SB) Q T 6 (6 players)
BB checks, UTG checks, UTG1 checks, UTG2 checks, Hero bets, MP3 folds, BB calls, UTG raises, UTG1 calls, UTG2 folds, Hero 3-bets, BB calls, UTG caps, UTG1 calls, Hero calls, BB calls.

Turn: (13.25 BB) T (4 players)
BB checks, UTG bets, UTG1 folds, Hero raises, BB folds, UTG 3-bets, Hero 4-bets (?), UTG calls.

*Not sure of the specific rules in this situation in this cardroom, but I believe the betting is uncapped at this point. I don't know if UTG realizes this.

River: (21.25 BB) T (2 players)
UTG bets, Hero...

6 but fold to 7.

tbh tho, I would raise and just call a 3b, expecting to lose if villain is so passive.

*G*

... tries not to get any vomit on his clothes?

If UTG is very loose, but is very passive and capping this flop, I'd put him on any 2p or trips on the flop. Minus the impossible QQ, and the in hindsight impossible TT. That leaves:

66 (3), QT (1), Q6 (3), T6 (3)

Unfortunately Q6 looks less likely because of his turn 3! when Q6 would be counterfeited, and 66 looks less likely because of his river bet when sixes full would be counterfeited. But with this pot being bigger than Ramon Escalante's rap sheet (well, it's ... long), I still call on the basis of the occasional WTF moment. Like he thought his sixes full were still good or something.

I would probably 7 bet the turn at least. The river is just a call though.

And discretely wipe the tear from your left eye when doing so.

yup