I have been reading in many RV blogs and forums that regular household toilet paper can be used if, when tested, the paper dissolves immediately and completely in a glass of water. Scott Tissue seems to get recommended a lot. Until recently, I have felt this advice was either wrong or incomplete. It turns out, it was in fact incomplete. To use household TP, it is safest to use 1 ply rather than 2 ply as well as pass the water test. AHA! That makes quite a difference. So, I went out and bought a multipack on sale of Scott Tissue 1000 rolls which is 1 ply and the package says it is septic tank safe. A quick test in water made it dissolve faster than a pack of RVers after a pot luck. It was fast! After a week of testing, all seems to be well and my bum is happy with it as well. I know my wallet will be happier too and I can find this TP anywhere, no special store required.
Now I hear some say that you can use 2 ply as well if it passes the water test. While this may be true, I think it would depend on the users. If you have someone in your rig who likes to use an awful lot of TP every time they go or a female who is still having periods (thus requiring more TP), I think it is safer to go with the 1 ply. The amount used at one time and how much water each person uses to flush will make a difference.
Don’t forget personal preferences. For some folks, their precious butts must have extra soft, 2 ply, fancy pattern, expensive TP. Convincing them to use anything else simply is not possible. If buying them ridiculously expensive special RV toilet paper makes them happy and keeps them off your butt, then it is worth it.