Here's a relatively tough hand in a situation I often have trouble navigating—flopping a strong hand on a monotone board.

V1 is a young TAG with a low VPIP, $800 stack.
V2 is an old man but not an OMC—plays lots of hands passively, but doesn't raise unless he's strong. When he hits something, he tends to aggressively raise it for fear of being drawn out on. Likes to call with draws. $1k stack.

V1 opens to $20 from MP. I call from HJ with 7c8c and V2 calls from BTN. Both blinds call.

Flop ($100): 6s9sTs

V1 checks, I bet $80, V2 calls, blinds fold, V1 calls.

I was surprised that V1 didn't c-bet, but that makes me think he has an overpair with one club. V2 probably has one high club as well, or possibly flopped a set (I don't think he'd raise a set here considering his fear of flush/straight). This is a clear value bet IMO, targeting flush draws, overpairs, and sets.

Turn ($260): 9c

V1 checks. Hero?

Here's where I wasn't sure what to do. Obviously flush draws can still be out there, but someone might have just boated up.

If I bet, how much? Should I ever just check behind here?

fold pre
flop bet is far too large
in mw pots, esp oop, you want the size of your bets to reflect your equity share , so you need to bet small. equities will shift significantly on turns on a board as dynamic as this one so you really don't want to bloat the pot with a mediocre hand, which is what your flopped straight is here
ap you can continue to bet turn small and plan on folding to raises
you can also x to c/c ,but you're prob better off b/f vs weak opp based on your reads that v2 that he won't bluff or vbet thin enough

Your hand is the nuts against a check/call small to the river range, but is usually drawing dead in a big bet/raise scenario anywhere in the hand.

Something like a $30 / $60 / $90 line is way more profitable than bombing anywhere, and you can do it on almost all non spade runouts.

Why bet small? They're not folding a large club or set and I guarantee flushes are raising me—both players are the type to bet big or raise with a flush for fear of getting drawn out on.

When you bet 3/4 pot or more. Your going to get passive calls from a lot of strong hands. Zero chance they raise nuts and likely to afraid to raise small flush. So your read is likely off. Both these guys can still have flush on turn.

Turn card sucks. As now they can also have boats. Luckily we are at bottom of our value range and can easily bet/fold and get value from spade draws still.

There's a possibility they could have a weak flush, but absolutely no chance they have a strong one. Both are terrified of being drawn out on and bomb the pot with strong hands.

Ex. V1 flopped top set on a flush draw board and immediately overbet pot.

What turn sizing would you choose?

Really? I disagree completely. Nut flushes are not the prime candidate for slowplaying even if they are nearly unbeatable, because another card of the same suit will likely kill action and cost the nut flush all future bets. You want to get as much money in as early as possible with a big flush, and OTF is usually a good time because flopped flushes are so rare that a lot of people won't believe you, or they call big bets with 1 big card of that suit. Also, you might be against a set which has pretty good odds to draw out on you but are likely never folding; get that money in ASAP before you're faced with a tough decision of whether or not to fold your nut flush to a big bet when the board pairs; it's generally a bad idea to slowplay a flopped flush, small or nut.

Who's afraid to raise a small flopped flush? I think even most OMCs would, and neither V2 or V1 are nits.