What chemical would you soak a master cyl in?

I have been tumbling stuff in Hot Water, Stainless Steel Pins, dish and Lemi-Shine (mild acid)
If to large to fit in my tumbler just soak in Hot Water, Lemi-Shine and Dish Soap over night. Real Rusty gets longer. Yes the water gets cold but starts out hot.
Or like stated ultrasonic for more gental