leaking return valve

I have a pool built in the 70's, inground, 15x30, that i just had redone. The only thing I overlooked ( having never owned a pool ) is that one of the return valves was plugged off with a screw in cap inside the pool. After a year of pool fun i bought an automatic cleaner, Hayword, and noticed that the pump tended to surge and the cleaner did not work right. Seeing how my pool has 3 intakes, main drain, skimmer, and vacumn line, and only one return i decided to fix and or check the return line. The line was not piped in and was capped off under the concrete deck by the pool. I dug up the line and repumbed it only to find out that the line had a leak around it where it comes out of the concrete that makes up the pool. The leak stops when the return is capped off with the screw in plug from the inside of the pool and the return jets out fine when the pump is turned on now that i repiped it but it leaks out of the backside of the pool under the pipe. How do i fix this? Do I fill in around the pipe with some kind of concrete or what? Any help would be appreciated.

any help??