go to any automotive paint store, like paint circuits, and pick up some rust removing acid… then just get any ceramic bowl and dip only the metal parts in
the problem with the sender is part of it is plastic and epoxy, and I don’t know how that or the diaphram inside is affected by any acid exposure
btw you can use this stuff safely with bare hands, as long as you rinse with plenty of water and a bar of laundry soap (not regular soap) or alternately baking soda