Yes, you can absolutely use KBS Klean on the plastic and metal parts on the inside of the tank as KBS Klean will not harm plastic. You can also run KBS Klean safely through the fuel pump to clean it out.
KBS Klean Product Link 👉 https://www.kbs-coatings.com/kbs-klean.html
Tank Sealer Kits Link 👉 https://www.kbs-coatings.com/tank-sealers.html
Please thoroughly review the Tank Sealer Directions and let us know if you have any additional questions.