Set of 3's Turn Play

[GTSamIAm]

I'm dealt 33 UTG at a loose table with little raising preflop.

I call. MP1 calls. MP2 calls. CO raises. Button flat calls. BB calls. I call.

Flop is:

K32 with two diamonds

BB bets. I raise. MP1 flat calls. MP2 folds. CO reraises. Button folds. BB flat calls. I cap. MP1 flat calls. CO calls.

Turn is the 4 of diamonds.

What is my optimal turn line in this multiway pot? Obviously I'm getting odds to draw to a boat if someone has a flush. Given the amount of action on the flop, it seems very likely that someone hit their flush, so playing this hand strong may be a mistake. Any comments?