Sorry I was just quoting the engineering reason for a p-trap. On a power boat
, sure it might keep bugs out. On a sail boat, heeled over, the p-trap will drain most if not all the water out and will not be filled till its used again. I would be only slightly worried of the stains from tooth paste, soap, etc staining the hull
Needless to say the p-trap came into existence, not to keep rings from going down the drain, but to keep methane from the sewers out of homes and businesses. Generally if you run water down the drain a ring would be flushed out of the trap anyway.
Bugs generally just come in the open hatches anyway. Least they do on my little boat.