I am in the process of switching to fly sparging and am converting a beverage cooler to a HLT. Based on the way the cooler is setup, I think my best way to connect it to the sparge arm is to run a short piece of 1/2" CPVC through the wall. There is already a rubber washer installed in the cooler that goes to the inside wall. I can slide the 1/2" tubing in there and it forms a pretty tight seal. However, it isnt water tight and will leak.
So, I am planning on using either silicone caulk or aquarium sealer to seal the small gap between the edge of the pipe and the rubber washer. I am assuming that both would be safe to use in the HLT, since they will only be in contact with the hot water.
EDIT: What about plumbers epoxy?