Looking for a word for an "outhouse" inside the house

I need a word for a restroom that does not have running water - where there is a pit toilet or a composting toilet instead of a flush toilet. If it were detached from a house, I am sure it would be called an outhouse. What is it called when it is in the house?

So the function of the room is the same as a restroom, it is the room where you would go to relieve oneself, but the facilities in the room are incongruous with the present definition of a restroom.

I am sure that people had such room prior to the invention of plumbing, but I cannot find any mention of it.

We have created such a room in our house for when the electric is out - which means we do not have water as we are on an electric well. But we are at a loss as to what to call it because it is definitely not a restroom.

Privy gives the sense of having a room with a non-mechanical toilet. While this is often a synonym for outhouse, the description doesn't contain the notion of being outside, so it retains its validity for an indoor model.

The usage derives from its being a place of privacy to do one's business.

Toilet also has validity here. The room can be named for the appliance whether it's a flush toilet or not. Interestingly the word derives from:

French toilette cloth on which items used for grooming are placed, from Middle French, piece of batiste, from diminutive of toile cloth.

Latrine can be used to describe such a room. By itself, latrine can refer to something either indoors or outdoors (e.g. Mediterranean, Malta or undulant fever, 1897 uses it to mean either, mostly hand-flushed), with outdoors being more likely for obvious reasons.

A bit more unambiguous is indoor latrine:

If you had to go to the bathroom, there was an indoor latrine, half a flight down. You would go in, take the wooden cover off a hole and sit on it. —Intrigue, Capitalism, Love: My True Story