Do you carry a toilet brush in your luggage? I once used a toilet in a vacant Roomette, and in retrospect see that it was not a very good thing to do. Also, since becoming a member of this forum, I have learned that using an unoccupied room on a train might be considered a felony.
Toilets notwithstanding, when I share a roomette, I have many times sat quietly in the room across the hall and I've never once had an attendant question it. I make sure I keep it spotless.
Just a side note here regarding the Viewliner bedroom bathroom. Discovered on the Lake Shore Limited and Crescent last October that the bathroom door does not clear the single seat - the seat must be moved out of the way to fully open the door. We wound up opening the door all the way and putting the seat back in position and leaving it that way for the entire trip.