Kashering a nife

Question

Ka vod Ha rav Can a stainless steel knife with a plastic handle that was washed in a non- kosher dishwasher be kashered. If so how? As far as I understand, plastic is not kasherable so even if the knife's blade is kashered could you wash the knife in a kosher dishwasher or with a kosher sponge without compromising the kashrut of any other item it is washed with. Would the same apply to a pot? Than You.