I started smelling a little head odor recently. I quickly traced it to the "duck bill" valve on top of the vented loop on the discharge hose. Like joker valves, these often overlooked valves can get scaled up and leak.
To confirm, I dried the top of the valve cap assembly, gave the head a few hard pumps on wet flush and checked it. Sure enough, the top was wet. Over time, this small amount of black water leaking into the boat will result in an odor. Depending on the manufacturer of the vented loop, replacing the duck bill is usually easily done. Mine is a Forespar MF-841. readily available for about $12 on Amazon or eBay. I've replaced it at least once in 20 years. Hope this benefits the list. Dennis C. Touche' 35-1 #83 Mandeville, LA
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