Re: is it necessary to clean the gas tank before first run?
I always remove the brass screen and install a FRAM automotive fuel filter before installing my fuel tanks.
My 4-liter Happy Time gas tank was used, and had sat for a while, before I put it on my bike. I also installed a locking gas cap, which involved filing the notches/tabs on the gas neck to accept the cap. Even though I put napkins inside the tank to catch the filings, I still had to clean it.(I should've inverted the tank while I was filing the gas neck.) After removing the petcock, I filled the tank with water several times and sloshed it around. Then I stuffed several napkins to sop up whatever was left in there. To ensure all water was removed, I stuck a hairdryer nozzle into the neck for several minutes. The tank became very hot, which evaporated any water that had been in there.
Any leftover metal filings or rust would be picked up by the $5 filter, although I can't see any crud in the see-through FRAM.