Hal, et al, The biggest problem is getting the 'fill material' to bond to the pipe (the pipe is smooth and doesn't bond well to crete or hydrolic cement. The core drill is not going to be the exact size of the pipe (you probably don't want it to be because core drilling 'dead level' is neigh impossible, so a little 'over sized' hole will let you level up the faceplate). once the pipe's hole is through the wall, you'll want to bevel the inteior wall so that you can pack in the filler and end up with the plate flush with the wall.
The plaster (I assume you have a plaster finnish) will be the first line of leakproofing. However, plaster is a crete product and the bonding issues can occur. What I've done in the past is to get some 2 part epoxy adhesive and apply it to the pvc pipe just prior to 'packing in' the hydrolic cement - the epoxy readily adheres to both the pipe and the cement providing a good seal (the epoxy adhesive is NOT the same as the 2 part epoxy putty which has been discussed other places here!) (There are some tips on doing this if you'd like them, but being a slow and poor typist, I'd just as soon wait for the request for additional info

). While I can not guarantee that NO water will get out using this method, I strongly doubt that you'll be able to notice any discernable amount leaving the pool.
If you've further questions about what I've said, feel free to ask for clarification. (and I look forward to any responses from the folks who have done this in the past decade

- which I haven't, I left crete pools behind in the mid 90's) - Best of luck!
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