Use a 2" drill, after drilling open up a little cave around the opening about 1 1/4" wider on each side and 1" back into the beam. Heap some marine epoxy around the 1 1/2" pipe about an inch back from the back of the cave, push it in and then fill the last inch around the pipe with the marine epoxy. Cut your pipe flush with the wall and glue on a wall fitting the next day after the epoxy has dried. Fill in the cave with either pool mix and white portland or buy a little tub of "Pool Patch" It's a high calcium quick setting pool mix. This is a 24 hour start to finish repair and it won't leak. With the right size cave you'll only slightly see the blend outside of your wall fitting where it meets the plaster. To small of a cave and you can't work the pool mix behind the wall fitting and into the cave.
This sealing method is the way you do it if your adding drains or returns into a wall on a pool that the buyer doesn't want to pay for a replaster job.

See ya,
Kelly