Solar water heater update

It became apparent that the solar hot water heater I built from recycled materials had a problem. I noticed that there was always moisture on the lower sides of the tank and a small puddle on the bottom. I gave it over a week to dry but it never did. Obviously, it was leaking. All the plumbing joints were tight so there was some sort of problem inside the tank. I decided to remove the tank and replace it with another recycled one that was in better shape. I closed the valves to remove the heater from the system and was quite excited when I broke the connection on the hot water side at the tank. The water that spurted out was hot enough to shower in! I drained the tank and used the water in the garden. Even the water at the bottom of the tank was lukewarm. This was after only a half day of sun. I'm sure that the constant moisture on the outside of the tank was cooling it as well so I have high hopes for the system with the new tank.