Gday bolero
Try soaking an old rusty tool tool over night. Brings it right back.
The acidic nature of vinegar gently dislodges any rust and gunk.
If you have an old kettle that’s blackened on the inside over time Cut a lemon up and put it in the kettle and bring it to boil for a few minutes and then have a look at how clean and pristine inside the Kettle is the lemon acid gently removes all the buildup it’s pretty much the same when you use vinegar in a tank but you may have to leave it in there for a while and slush it around
Cheers. Hughesy