OK, here's where you old salts can set me straight.
Visualize an impeller pump as being a T...with the vertical part of
the T being replaced by a circle, i.e., the impeller. Now assume the arms
of the the T are labeled IN/OUT (left) and OUT/IN.(right)

The question is...for a given rotation (direction) of the impeller,
which direction is the water going to flow..and which direction
should the impeller vanes be flopped...with the rotation or against
the rotation..if that makes sense.

An ancillerary question....before you install the pump, do you
need to fix the impeller vanes properly depending on the
anticipated rotation? And if you don't...what happens?

Thanks
Norm B