thats exactly what I was thinking, A polyurathane caulk around the tip of the pipe where the plaster ends. Except I didnt really want to "void" my warranty or whatever those subs call it. so I left it be and they came out!. They found the leak with a syringe and food coloring, And fixed it with A+B putty epoxy. They guy that came over to fix it accidently left a whole package of the stuff behind. So I tried the putty on an old brick and about an hour or so later the stuff is hard and almost impossible to pick off the brick. It's been about 10 hours since the job and still the same water level. BTW that epoxy cures underwater, and on the lable of the stuff it's accually designed for pool leaks sticks to concrete, metal, pvc, wood, so just about anything. Great stuff.