It is a simple process, I used the same polishing compound / cream that I use to polish the stainless steel parts.
Just put some polishing cream on a rag or microfiber cloth, then polish the clear
tank as if it was a stainless steel
tank, I did it by hand, turning the tank with one hand while holding the microfiber cloth with the other hand, it takes like 20 minutes.
Same with the internal of the tank, Insert one finger covered with the microfiber cloth and polishing cream, and with the other hand turn the tank.
Some friends used toothpaste instead the polishing cream.