So i started the process of filling the dent in the tank today, i began by sanding the dented area and the surrounding area with 80 grit to give the filler a good surface to adhere to, i mixed up a small batch of filler at first so to just fill the dent, once it had sat for 20 mins i started sanding it down with 120 grit, when i felt it was smooth i mixed up another batch and filled the dented and surrounding area with enough filler so that i had enough outside the dented are to feather it back smooth and even with 120 grit then 320 grit, i have a lil more sanding to do before i lay done a layer of primer. Here are some pics of the process.