This is the back of a home of a wealthy family (the Bordens) in New England from the 1890s. I read that the house had no toilets/plumbing. In this & another picture I see no detached outhouse - would this little thing on the back of the house be an outhouse? I've never seen an outhouse for a wealthy family. Seems kind of elaborate for a door to the basement. Too small for a shed & there's a small barn there anyway.

Or would they have just used pots & tossed it out later?

Hard to tell. 

 

However, I would think a "well to do" family would have servants and the family members would never use an outhouse, unless you had to do a No.2  Also an outhouse usually have 2 (or 3) opening.  One inside, where you would enter from a shed and one outside behind so that a person could clean out the "waste".  A wealthy family may have a double, where one opening would be adult height and the other child height.

 

Remember people only took a bath once, on Saturday back then, so bathrooms weren't needed.  You simply "washed up".  A person would use a commode, chamber pots and possibly chamber cabinet.  Some wealthy victorian families may have had a "curious" cabinet, which housed a commode and chamber pots, etc. hidden in a cabinet.

in 1890 having indoor plumbing would have been rare, even for an expensive home or wealthy folk.