Yep, Richard...I suspect some waste is
getting into the upper part of the pump. That the odor went away for even a short time after you flushed out the intake pretty much confirms it. Water--even fresh water--sitting in the summer heat in an anaerobic environment is gonna stagnate and stink...and the warmer the weather, the quicker it's gonna happen.I am NOT a fan of just closing the intake thru-hull and adding water directly to the bowl to flush. For one thing, it's a PITA to have to do...for another, it keeps any water that's ever gotten into the intake sealed up to turn into a primoridal soup. And on small boats, it means sacrificing an already limited supply of fresh water unnecessarily.There are several ways to eliminate sea water odor...one--teeing the head intake into the head sink drain line so you can flush the sea water out of the whole system before closing up the boat--is described in my book ("Intake Odor") and also posted here many times, so can also be found by searching the archives. If that won't work on your boat (no head sink or sink and toilet are on opposite sides of the keel)...a 3/4" y-valve, a short piece of hose and gallon milk jug will accomplish the same thing--when closing up the boat, after you've closed the seacock, fill the jug with clean fresh water...stick the hose in the jug, turn the wye valve...flush the toilet.If you're determined to flush only with fresh water, install a separate 5 gal water tank that is not connected in ANY way to your fresh water system to supply it. Even a bladder will work for this, and a bladder has the added advantage of not requiring a vent (unvented bladders can ONLY be used for fuel or water, NEVER waste!). The most difficult challenge when it comes to adding a flush water tank is filling it...you can't fill it from your fresh water system...adding another deck fill is a PITA...bring a hose into the boat to fill it is an even bigger PITA. But--thanks to some discussion on another board about this same issue--I THINK I've come up with a solution that'll work on most boats...it doesn't conserve any fresh water, but it's a lot easier--and keeps the system rinsed out--than adding water to the bowl: Instead of the usual 1.5" fill, a 3/4" fill (use a reducer if necessary)...using a 3/4" y-valve, connect the fill line to any sink drain line that you can access and still put the tank in a location that will also allow you to connect the toilet intake to it. When you need to fill the flush water tank, turn the y-valve, run water through the sink. Keep the y-valve aimed at the thru-hull except when filling the tank. Before someone asks..."recycling" used wash water, shower water, etc for toilet flushing would only create a new version of the problem you're trying to solve, 'cuz "used" water is full of bacteria, soap scum etc that create smelly sumps. So it's gotta be clean water.As for your macerator question, as long as the motor runs and there are no signs of corrosion in it, a new impeller every year or two should keep it working forever. Flushing it out with clean water regularly--another reason to flush out the tank regularly--will eliminate any sludge that can clog it and also prevent the impeller from sticking to the housing (which can crack the impeller). So I suspect you don't need a new one, yours just needs a new impeller and a "bath." Impellers don't last forever. Every time it has to prime, the impeller has to run dry first. Even if only for a few seconds, that dry friction wears the edges of the impeller vanes a little...and a little more. And the more the vanes are worn, the less and less efficient the pump becomes...till finally, the impeller can pull anything through the pump any more. This is wear that cannot be seen just by looking at the impeller because it's too even--no signs of "fried" neoprene...so an impeller may LOOK fine, but the difference between impeller vanes that fit the housing tightly enough to pull ("impel") waste through the pump and vanes that can't pull anything through is only about twice the width of a human hair. So replace it at least every TWO years--every spring is better---as preventive maintenance if you want your macerator pump to keep working to spec. And THOROUGHLY flush out your tank and macerator at least 3-4 x/year.