Unless you've been filling your tank with unfiltered third-world gasoline, I can't imagine it needs to be flushed out. At the most, maybe swish the the small amount of gasoline remaining in your tank around and dump it out into a suitable container.
__________________ When you have a choice, buy American.
You can easily peer into the tank when the pump assembly is removed. It is easy to get your arm into it and use a paper towel to wipe it up some should it be necessary. Hopefully nobody has put some special "fuel additives" into your tank. I use a locking cap to avoid such miscreant activities!