On one of my Texas Eagle runs, when I boarded Southbound at FTW, my attendant said the upstairs john was out of order and to use the downstairs ones. No problem. At SAS, I got off for a while, and when I got back on, as I rounded the top of the stairs, the stool was in the corridor and a maintenance worker was snaking the hole. About the time I peeked in, he got a "bite" and when he reeled in, started on a tirade about certain women's products. So it seems like they don't have unlimited flushing power and those signs posted about not flushing certain items are gospel.