...So I began to repair the tank. I am not done yet so this is an attempt to fix it.
The first thing I did was to clean the tank with electrolysis. I learned this method from watching youtube videos. It works far better than I thought it would so it is my default method until a better way presents itself. (If there is one.) Normally you would want to repeat the process until the tank is spotless on the inside but I am going to have to leak test it after I am finished and this could be a great way to do that.
I explain this simple process in the videos:
To fix the dents I have drilled holes into the inside of the tank where they will not be visible after assembly. This gives me access to the inside so the dents can be tapped out. Later I can plug the holes and seal them with aluminum braze. I devised this method myself because I do not have a welder. Normally you would want to cut a section of the tank out to get access to the inside. After the repair you weld it back together. The holes make it hard to find the exact dent you are looking for because you can't see inside.
Unfortunately I forgot to take a picture before I began, but if you watch the video of the leaky poppet valve in the last post you will see this particular dent before I touched it. Here is a series of pics illustrating how I have tapped the dents and sanded them smooth. You need tap then then sand repeatedly: Tap sand tap sand etc. Sanding helps the low spots stand out so you know where to tap next.
I still have to fix several other issues so the tank will be a lot of work. I will post pictures when
I am done no matter how good or bad it looks.