i’m doing the fuel tank clean and seal. the fuel tank is from a pickup truck that sat for 23 years. so far i used soap and water, metal wash, and muriatic acid. the tank is still not coming clean. i don’t want to move on until i get the tank completely clean. i understand that you have to complete each step in order. i did the metal wash twice and left the muriatic acid in over night, and the tank is still not clean. i stuck in a rod and scraped the bottom of the tank and it is still gooey. what do i try next?