Check-raising the river rarely works for me but here I thought I should give it a try, one of them had to have a flush. I'm not sure about the amount to raise though, I guess I only need to give the first fish the right odds to call, and the other will follow.
PokerStars No-Limit Hold'em, $0.10 BB (9 handed)
Hand History Converter Tool from
FlopTurnRiver.com (Format: FlopTurnRiver)
MP3 ($10.35)
CO ($0.55)
Button ($3.75)
Hero ($17.95)
BB ($4.80)
UTG ($5.85)
UTG+1 ($2.50)
MP1 ($10)
MP2 ($5.75)
Preflop: Hero is SB with 6

, 6

.
UTG raises to $0.2,
2 folds, MP2 calls $0.20,
3 folds, Hero calls $0.15, BB calls $0.10.
Flop: ($0.80) 4

, 9

, 9
(4 players)
Hero checks,
BB bets $0.2, UTG folds, MP2 calls $0.20, Hero calls $0.20.
Turn: ($1.40) 6
(3 players)
Hero checks,
BB bets $0.4, MP2 calls $0.40, Hero calls $0.40.
River: ($2.60) 3
(3 players)
Hero checks,
BB bets $1, MP2 calls $1,
Hero raises to $3, BB calls $2, MP2 calls $2.
Final Pot: $11.60
Results in white below:
Hero has 6d 6h (full house, sixes full of nines).
BB has 9s Kh (three of a kind, nines).
MP2 has 6c 2c (flush, nine high).
Outcome: Hero wins $11.60.