@Lizzie I'm on a private septic- I explain to my guests that while it can handle toilet paper, I try not to overload it, so nose-blowing paper, women's pee paper, etc, should go in the basket, and that all the rest can be flushed.
And septic systems work best the less water goes into them, so no need to flush the toilet everytime they have a little pee. (If it's yellow, let it mellow)
Everyone's been fine with this, but it's easy to forget (we just put all the paper in the toilet and flush everytime automatically, without thinking, if this is what we're used to) so I also let them know that it's not the end of the world if they forget.