TM3023 2004 Toilet Question/Problem

It's been a while since I posted here on TMO but in the past, I have received great answers so here is my current question. On the recirculating toilet, the inside pull valve no longer seals the toilet from the drain pipe below. ie if I close the inside valve and charge the toilet, then go outside and open the black water valve, the toilet drains (slowly). My diagnosis is that a piece of toilet paper may be keeping the inside valve from closing completely. (just a guess since it feels like it is not closing completely). So, I am seeking advice on a possible fix. Would there be any chance of adding some chemical that would "dissolve" the tissue? Is it a monumental task to tear apart these toilets? Any other clever idea? TIA for any advice.
BTW, I have logged about 40K miles since I bought in 2004. Fantastic trailer. It has been up and down the Rocky Mountains and 5 trips from Texas to NS Canada (we basically live in it for 2 months in Canada) Various Texas WE trips including Padre Island National Seashore. Had a blown tire at 60 MPH without mishap. (my fault for not replacing the inadequate rubber valve stems on the original tires). New rim, two tires and 3 steel valve stems and all has been fine since. No other big failures. Just the usual loose screws, stove coming loose, slow leak in under-sink plumbing. All in all a great experience.
Cheers