Flushable wipes should never even go in your stick and brick toilet, let alone in your RV toilet.
In over 15 years owning my trailer I have only once ever had something spill out when I open the cap. I'm pretty sure somebody on the storage lot pulled the handle as a joke on all the stored RV's. Other than that the drain pipe is always dry when I remove the cap. I would say if you have more than a few teaspoons full of liquid drain out then you have a valve leak.
Next time you dump flush the tank a few times while rapidly cycling the handles to try to dislodge the paper stuck in the groove. If that fails you can either replace the gate valves or add an additional valve at the cap.
Replacement gate valveTwist on valve