The worst problem with a concrete tub, is heating it. If it were a hot tub, it would be constantly heated and ready to use.
Since this is a tub, you will have a hard time overcoming the solid mass of concrete that will be needed to be brought up to temperature.
This is what I used when I wanted a tub like that.
They make cable waste and overflows that may reach high enough.
or in my case, I bent some some copper rod and extend a PP W&O.
You could also use standard glue type W&O fittings.