28' is a bit big for a portapotty
It's likely to devalue your boat. So before you toss the "baby out with the bath water," let's look at the reason you've had so many problems with the toilet. Unlike household toilets, marine toilets have a finite lifespan that can range from about 5 years for the cheapest toilet to over 100 for $1,000 toilet....average is about 10 years. Boat builders don't use the most expensive ones, so if your toilet is still the original, it's a pretty good bet that it was totally worn out when you bought the boat. Most likely the hoses were also already permeated with odor too. So it's not surprising that you've have nothing but problems and and stinky boat. A 5-6 gallon portapotty, permanently installed and fitted for pumpout, plus a macerator to move its contents to your larger holding tank...you'll also have to replace the hoses too, if you want to get rid of the odor--will cost you about $400. For about $300 you can replace your toilet with a Raritan PH II--about $200 and rated the best manual toilet under $500 for a couple of decades and your hoses with AVS96, which has proven to be at leat 16x more resistant to odor permeation than any other hose. Or you can spend $50 at Sears for a 2-3 gallon portable portapotty that has to be emptied every weekend.Btw...I see you're on Lake George, one of the only lakes in the country where gray water (galley, bath and shower water) has to be held. Do you have a separate tank for it, or is it also going into your waste holding tank? If it is, that can also be a source of your problems.