Greywater Tank outlet connection

[BBBlue]

What is the best sealant/caulk to seal/caulk the outlet pipe connection to the greywater tank. I had a leak that occurred when the outlet pipe started to back out of the tank outlet. The outlet appeared to have some sort of caulk and a large hose clamp around the connection, from the factory. I have tried a couple of different items to seal the connection (Proflex and a rubber sealant) which has failed to keep the pipe in place when the tank is full. In addition, I found a hairline crack on the tank, which is polyethylene, and cannot find anything that will stick to the tank. Tried JB waterweld, and eternabond tape without any success. Any assistance would be deeply appreciated.