I have a stream ,panfish type tackle box a lot of mepps spinners and small spoons of various shapes and sizes some of the spinners are 50yrs. old. tumbled them all including buck tail spinners, they came out looking like new even cleans the buck tail . Of course had to tumble some longer but had no problems tumbling them over night. Try tarnished plugs works great.
indoor boilers require about 1/2to1/3 of the wood to heat a home that an outdoor boiler uses ,heated my home with one for 40yrs. list it on heating help .com classified
i my be wrong but it looks like that fitting would have a nut on each side locking it in place on the tank .you may have to go in through the sending unit to undo it. i would try to loosen the nut with out turning the pipe fitting.