My 3800 has the same arrangement. The refer and shower have "grey" water that should be kept out of the bilge. The bilge should only have water from tank overflow or rain water down the mast and should only be clean fresh water. Same for a leak in a water tank draining into the bilge. Easy check for a leak is to taste the bilge water (at least if the boat is in salt water). Good reason to keep the bilge clean.