Salt water only in compartment #3?
If you’ve been sailing on a port tack or a following sea, water will siphon from the separate electric bilge pump exit on the transom back into the bilge. I believe all the walk through transom boats have the electric bilge drain “T”ed into the manual drain which is high enough to prevent back siphoning. If this bothers you, install a one-way valve in the electric bilge pump hose. If I find salt water in only #1, #2, and possibly overflowing into #3, I look at the depth and knot log transducer fittings which are located under the forward settee.
