As Brian points out, and is required, you MUST have a siphon break for all drains that are below the water line. This wouldn't include a recirculating line (like an engine or refrigeration discharge) -- but clearly a bilge pump should one whether it's above the water line or not.

Just because you can't see the water burbling in the sink, doesn't mean it isn't going to be above the "T" you are considering in the sink drain.

Depending on a check valve is a not the way to go.

While you may believe that "less is more" when it comes to thru-hulls, I'd advise you not to trade a fear for a living nightmare.