There are two ways to go with the two ply. It is very easy to just use one of the plies by just separating them as you pull the tp off of the roll. That way it costs less for the two ply vs what you can buy in the RV places and it goes twice as far.
However we use the strong quilted stuff that you see the bears use on TV. It don't fall apart like the other stuff does. Our solution to not messing up the holding tanks and valves with toilet paper is simple, in fact we have a septic tank at home and practice it there as well, The used tp goes into one of those small trash buckets with the flapper top. It may sound gross and all disposing of tp that way
, butt we also empty the trash bucket once a day. We use the plastic grocery bags for liners and tie them up real tight when we toss them.
The best way we have found is to not put anything in the toliet that does not pass through your body first.
That is my story, and I am sticking to it.