Possible old outhouse site

Possible old outhouse site

I have been trying to figure out what a cement trough behind my 1850’s house could be, and it has been suggested that it was a outhouse pit.
The reason we are not sure is the curved part at each end. I have looked online and all pits seem to be square or rectangle.
So I wondered if you had ever come across a outhouse cement pit that was shaped like this?