as you are changing your tank, flush the pipes too
connect a pipe from the pump into a jar of clean fuel, disconnect the pipe from the fuel filter on the metering head and put it another jar. run the pump for a bit
also change that big fuel filter
and change the filler neck for a stainless one. it's the filler neck that creates all 90% of the crap in the first place!!!
you could clean the existing tank though, and it would probably be ok