The selector switch(wet/dry) only allows/not allow fresh water to the bowl, when actuating the pump.
Jasbco does have a rebuild kit for the pump. I wish I would have known last spring, I bought a whole new head, jabsco had a parts list along with discriptions for rebuild parts.
Repair Kits Available for Jabsco manual marine toilet Models 29090-2000 & 29120-2000
A 29045-2000 Major service kit, pump
B 29040-2000 Pump Assembly
C 29094-2000 Valve cover & Handle assembly
D 29051-2000 Pump Cylinder Assembly
E 29047-0000 Bowl installation kit
Hope this helps. The rubber flapper valves I can see needing replacement fairly often, the ones I pulled out were fairly 'dry-rotted', a .50 cent valve and would have been back in service vs. $127 for whole new unit.

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2000 248 5.7L DP
'92, '94 SXI 750, '08 STX 15F, '12 Ultra LX 300
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