Welcome to the forum!

What sort of faceplate/ adapter will you be using on the interior of the pool?

Depending on your answer, hydrolic cement should be all you need. If it's possible, shove the pipe through the wall from inside the pool, after first packing in the cement, then use more hydrolic cement on the outside.

If you could provide a few more details as to what you're using, we can provide more detailed instruction on 'the best' way to accomplish your goals