We don't have the R25 but I'll take a stab at this. If it's the same as our R27 your toilet water comes from the water your boat is sitting in and not your water tank. If your R25 is the same then I'd guess the thru hull lever may not be open, therefore not letting water come into the system. Our R27 engine sea strainer services the water for the engine, head and transom wash down hose.....so if you're in the water and the engine is flowing water and your R25 is configured the same as our R27 then this is not your problem. Check to see if you have a separate sea strainer for the head and find the on/off lever to make sure it is in the on position. If you do and it is closed that would be the problem. If you do and it is open it could be blocked from under the boat by leaves or plastic and needs to be cleaned out. Please report back to us and tell us what resolved the problem.
Jim F