The weir is the flap that opens and shuts on the front of the skimmer that allows leaves and debris to float into the skimmer basket but then prevents it from floating back out.

As far as a gizmo or whatever in the skimmer, I don't use one. The water level is lowered below the skimmer and return so I don't feel the need.

I do not know what the "travel/storage retainer" is that you mentioned. Sorry.