Try DMSO!

The kind of contamination was not mentioned in the enunciate. ― Nevertheless, you may still want to check a few previous RG discussions:

https://www.researchgate.net/post/How_can_i_clean_my_teflon_autoclave_from_inside_contaminated_very_roughly_with_MnO2_nanoparticles https://www.researchgate.net/post/How_can_i_clean_Nanosticks_of_TiO2_from_Teflon_beaker https://www.researchgate.net/post/Someone_know_how_to_remove_VO2_from_a_teflon_linen_how_to_clean_it2 https://www.researchgate.net/post/cleaning_of_autoclaves_teflon_tube https://www.researchgate.net/post/Cleaning_of_CuO_synthesized_Teflon_container https://www.researchgate.net/post/Any_advice_on_cleaning_PTFE_liners_for_hydrothermal_synthesis_autoclaves https://www.researchgate.net/post/Do_you_have_any_suggestions_to_clean_pure_PTFE_having_metallic_residue_on_it2