"My Jabsco is now 17 years old and gives no trouble at all."
Not surprising because the ones that were made 15-20 years ago were actually made to last...whereas Jabsco toilets made in the last 7-10 years are purposely designed to be "disposable" because there's no profit in repair parts and service kits, only in new pumps. Thetford discontinued the whole Wilcox-Crittenden product line because W-C toilets for that very same reason. Unfortunately, marine toilets aren't the only things about which that's true.
I have never needed to replace the joker valve ...
If that's true, it's amazing that the toilet can flush at all...and it has to take a zillon pumps. The joker valve in ALL manual toilets should be replaced annually...here's why:
JOKER VALVE 101
Most people think that the only thing the joker valve does is acts as a check valve to stop backflow from returning to the toilet or odor from the tank from escaping through the toilet. But that's not a joker valve's most important function...in fact, the joker valve is THE single most important replaceable part in a manual toilet.
Here’s how the discharge half of the pump works: On the upstroke of the piston, a vacuum is created in the area beneath the piston. This causes the joker valve to close tightly, and the flapper valve beneath the pump to open, allowing some of the contents of the toilet bowl to be drawn into the bottom half of the pump. Then, on the down stroke of the piston, the flapper valve is slammed shut, and the effluent is forced out of the bottom of the pump, through the joker valve, and off down the line. But when the joker valve becomes worn and/or there's a buildup of sea water minerals on it, it can no longer seal tightly on the upstroke of the piston...less vacuum is generated when you pump it. And as it becomes more worn less and less vacuum, till finally the bowl contents simply move up and down a bit, but don't go anywhere. Sometimes the flapper valve needs to be replaced too, which is why toilets should also be rebuilt at least every 5-6 years as PREVENTIVE MAINTENANCE.
You prob'ly won't notice the loss of efficiency at first because it's so gradual...same as we don't see that we've gotten a little older than we were yesterday when we look in the mirror each morning. But I guarantee you that if it's been two years or longer since you replaced the joker valve, you need to pump the toilet at least 50% more times to move the bowl contents to the tank or all the way out the thru-hull....IF they're getting there at all any more.
Marine toilets have moving parts that require maintenance. PREVENTIVE maintenance is called that because it PREVENTS problems that have to be fixed. You get to do PREVENTIVE maintenance on YOUR terms, when it's convenient for YOU...unlike repairs, which NEVER are needed at a convenient time.
"...and only re grease the piston twice a year
It's not the piston rod that needs grease, 'cuz only things that rub against each other need lubrication...and the piston rod doesn't rub against anything...the seals, o-rings etc ON the piston rub against the inside of the pump cylinder wall. So it's the cylinder wall that actually needs lubrication. And it's easy to do. All toilets leave the factory slathered in thick non-petroleum based grease...buy a tube. Jabsco toilets: remove the top of the pump...Raritan PH II/PHC: remove the pump from the base, which requires removing 4 screws. Stick the nozzle on the tube into the pump an give it a HEALTHY squirt. Replace the top of the pump/put the pump back onto the base. BE CAREFUL NOT TO OVERTIGHTEN SCREWS! Pump a couple of times to spread the grease all over the inside of the pump...you're good to go for a year.
Steve... "We have one well know nsailor (that shall be kept nameless) on this site that has spent over $600 (and it may be growing) on Jabsco repair kits.
Not repair kits, new pumps, which cost about the same as a kit. And he's now spent over $1000 in new pumps for two $100 toilets.
Squid...if it ain't broke yet, don't fix it. When it does break, don't fix it...replace it. Meanwhile just keep it well lubricated.