When I was installing a new sink on the boat, the old one had a "trap" like the one in your house. I hooked the new one to it but kept wondering...why on earth do you put a trap in a boat? There is no "sewer gas" that will make its way to the sink, it drains overboard. Why not just install a drain hose right to the thru hull fitting and be done with it? I noticed it is not draining as fast as I would like and I think the trap is the culprit...I am thinking of ripping all that excess plumbing out and going direct. Any reason not to?

My two sinks dump strait out the side.
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Both mine dump straight out also, maybe your boat was previously owned by a licensed plumber?

The only reason why you could have a trap IMHO would be if your sink empties into the holding tank, then you would want a trap to block the gas/smell

No trap needed. Whomever installed it forget he wasn't working on a house. :)