You won't like it...'cuz recirculating means just what it sounds like
The system recirculates waste as flush water.In the 70s, some boat builders cobbled up recirculating systems using Kracor holding tanks, Raritan compact toilets and Wilcox-Crittenden fittings. The 5 gal tank was "charged" with a solution of chemical and a couple gallons of water. When the toilet was flushed, it pulled the "flush water" (chemical solution) out of the tank and discharged it--along with the waste in the bowl--back into the tank...which means that as waste was added, the "flush water" included an increasing amount of it. When the tank was full, it's pumped out and then "recharged" again. It barely holds enough to last two people through a weekend, and--especially in hot weather--it STINKS after about 24 hours. But it was an inexpensive way to install a complete system that didn't require any below-waterline thru-hulls.If that's not enough to convince you to to replace it...if the toilet is still original, it's worn out...also so old that no parts are still available. The tank MAY still be in ok condition, but all the hoses have to be so old and brittle that they should be replaced too.But on a boat that size, I wouldn't replace it with a typical marine toilet, tank, all the related plumbing AND necessary thru-hulls...I'd replace it with another self-contained system, i.e. the "MSD" version of a portapotty. "MSD" means it's designed to be permanently installed and fitted for pumpout. A 5-6 model will hold about as many flushes as about a 15-18 gallon tank connected to a manual toilet. You already have the pumpout fitting and the necessary vent fitting, so the only plumbing is the pumpout hose and vent line. No moving parts so--unlike a manual marine toilet--no maintenance...no tank and related plumbing eating a major portion of your storage space. Iow, all the advantages of a toilet and tank, none of the drawbacks. And at a fraction of the price.The SeaLand 675MSD would be a good choice...Thetford has several choices, including one "electric" version that uses 4 AA batteries (or maybe C cells).