We have always used the small wastebaskets in the heads for used toilet paper. We bring small trash bags from home (or Kroger bags) to line the wastebaskets, replacing as needed and transferring used paper to the main trash. We have a rule that nothing goes in the head other than pee and poop. We close the 'Y' valves except when dumping in the open. Not perfect, but seems to be the best option. The humor is when we return home and get momentarily confused about what to do with our used toilet paper :-)