To give the tank a shine I use a soft open mop on my bench grinder and buy the blue coloured soap which is for plastics(not the white one which is for aluminium). Please be very careful and do this process very slowly and do not press at all but just let the tank touch the mop as it is spinning. It is time consuming but well worth while. Practice on an old plastic tank because it is easy to burn/scuff. Use a new mop, not your old aluminium polishing mop unless you want your tank dark grey.