[Dino's A]

If I had to try to clean the tank while in the car,
I would first mask off everything around the tank top.
Maybe cover most of the front of the car. Empty the tank,
Then remove the shutoff valve and use a barb fitting
to a hose to drain it all when the flushing begins.

Then I would use a light duty pressure washer to remove all
rust and crud that is flaking off. You have to attempt to
attack every wall and bottom that you can. A strong flashlight
& inspection mirror is a must to continually inspect all areas.

Yes, I know, it's water! and water is the tanks worst enemy. But doing just that
for just a few minutes, it won't hurt. Now that all the flaky stuff is mostly gone,
I would use a solution of 99% rubbing alcohol perhaps with a garden pump sprayer
to flush out most of the water. Let dry, fill with gas, add a little MMO, and
that should stop the debris from ruining the gas.

Your strainer should have that newer style paper element in the bowl.
I also use another small paper element filter in line before the carb.

Clean gas is paramount. Now saying all this, It is not a complete
substitute for removing the tank.