I have an inground plaster pool, currently chlorinated by floating
ducks, and would like to install an automatic chlorinator - an
"off-line" chlorinator that connects to the main pool lines through
1/4" plastic tubing. Trichlor tablets.

The pool pump is powered down at night, and I need to figure out
what will happen with the chlorinator when the power is off -
whether the chlorine concentrate will flow back into the pump. But
what I can't find is a diagram or description of how these
chlorinators actually work.

If I were designing one, I think I would have a container with a
sealed lid at the top for adding the trichlor pucks. Then I would
have an inlet at the very bottom, and the outlet connected to a
standpipe. With the container being sealed, the incoming water
would rise to just above the level of the standpipe opening, and
the trapped air would keep it from going higher.

Is that how they work, or is it different?

So when the pump is shut down, does the water inside the
chlorinator just stay put, or does it tend to flow one way or the
other?

And does anyone have a particular brand they like?

Thanks for any insights.