I use my tub for plants when i go away on trips..a week at a time. i put them in the tub on top of plastic container and fill with hot water midway to that container. When I arrived home, the plants survived, but all the water has drained. Does that mean there is a leak in the drain? Its hard to tell with the tub into the floor.
Try it when your home? and time the process?
The "drain stoppers" (for lack of a better layman's term) on tub drain/overflows is not particularly good, for holding water over the long term. There are no gaskets, or seals, to prevent water from seeping by. It is basically, a piece of metal, blocking the pipe. The metal is raised or lowered, by the little lever.
Some newer drains (often called "toe poppers") that are NOT operated by a lever (instead you simply push them and they stay up or down, have a gasket that MAY seal a little better than the old style drain.
So to answer your question, the bathtub drain is not designed to hold water for extended periods of time. It's only designed to hold water long enough for you to take a bath...usually not more than an hour or two at most. So there is probably nothing wrong with your drain and not holding water over extended periods of time would, IMHO, not indicate a problem.
But not better than the 'really old' style drains. When I was a kid back in the 40s, the tub drain stopper was a white rubber tapered plug with a pull chain that was attached to the tub somewhere (forgot where).
Hot Water? Some purpose to this aspect?
Fill the tub with dirt....you can shower on your trip
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