As they have said the old days the potty flushed right out onto the tracks. One could flush and see the ties flying by down below. The NG in the 50-60's was this way. I vividly remember our trip to Mexico in 1963 where we rode for 2 weeks and most of that was in a section pullman the organizer had for us. It was a big restroom, but only one toilet. On the floor outside the toilet room was a large bottle of drinking water in a tilt rack. Of course a lot was on the floor while trying to pour on a moving train. I remember 611 and 1218 excursions in the 80's used ex N&W and Southern Cars, and they too went down onto the tracks.
Funny side story. In 1970 we were shooting pictures of the NRHS convention trips. I decided to take my super 8 (Silent) camera and place it between the ties under a bridge where it met the end of the fill. It was a doubleheader with 630 and 722. It looks like someone flushed as it passed over, but no solid stuff hit the camera!!!! I think early Amtrak trains also had the open end toilets, and at some time later started the retention toilets as they got their own more modern coaches.
Greg