Raritan electric toilet issue

[scross]

First cruise of the season in our 2017 C-28. We have the Raritan electric flush toilet in the head.
At dock there’s no issues. Flush operation works perfectly. Water for flushing comes in through starboard side seacock, through starboard sea strainer and then to the toilet as intended.
While underway at speed the toilet will slowly fill with clear, clean sea water which I assume to be from the toilets intake side. If you close the starboard sea cock prior to cruising there’s no problem. Repair shop says the Raritan needs a new joker valve.
I thought the joker valve was on the discharge side of the toilet to prevent back flow from the nasty black water side of the toilet back into the bowl.
Am I misunderstanding how the joker valve works?

Update: After reading through the Raritan manual, the toilet was not plumbed according to their specifications. To get into specs, FM appears to have used an inline pressure reducing regulator about 6” upstream of the sea strainer. The regulator FM used seems pretty unique. I’m thinking it failed. Speaking with the Raritan folks tomorrow to get the max pressure intake specs so I can start hunting for a new inline pressure regulator.

 

[marob]

We bought a new 2021 C28 and the toilet has been an issue from day one. It will slowly back fill the toilet with waste and last year Port Boathouse installed a joker valve which had not been installed at FM, it did not correct the problem and I was told by Port Boathouse this is a known issue and and that FM was supposed to be working on a fix. It has been 3 years now and still no word on what needs to be done. Still love the boat but unhappy with the response from the factory

 

[Traxxas]

Are you sure that thing isn't a check valve? There's one just like it on the aft bildge pump hose too.

 

[scross]

Problem now understood with easy solution.
Prior owner or the factory, not sure who, installed an 10 psi pressure reduction valve on the hose going to the toilet’s intake fitting. The pressure reduction valve failed, resulting in an over pressure on the intake line, but only when at cruising speed, going to the toilet.
This whole thing was not plumbed properly. The starboard side of my boat has two seacocks. The big aft one is primarily for the raw water wash down system. The aft seacock developes pretty high pressure when cruising. The forward seacock towards the front of the engine on the starboard side is an always low pressure feed for the toilet intake.
Right now my toilet intake hose is plumbed to the big aft raw water wash down strainer.
There should be a small inline Raritan strainer on the hose going to the toilet which is missing. There should not need to be a inline pressure reduction valve because the hose should be plumbed to the forward seacock.
There are a two other issues to make the toilet intake feed work easier. I’m going to continue to use a feed from the big raw strainer with an inline on/off ball valve on that hose and a T fitting after that so I can choose which of the two seacocks is supplying raw water to the toilet.
For normal use I want the feed coming from the low pressure forward starboard seacock. For winterizing I want the feed coming from the big raw water wash down pump strainer so I can easily run RV antifreeze through the hose to the toilet. Sounds complicated but a requires fairly simple plumbing solution.
Traxxas: Raritan does not recommend a check valve either before or after the strainer on the intake side.