What to clean gas tank with?

After the tank is out of the car.
I remove the sending unit and let the tank dry out.
Next I fill it with water and let it set for a few hours.
I load it up and haul it to the car wash and clean everthing out I can with the high pressure.
When I get home I put about a quart of pea size gravel in it, tape up all the holes and shake the crap out of it. This takes some time.
The I use a shop vac to get all the gravel out.
Another trip to the car wash and wash it out with clear water.
Final vacuum with the shop vac and inspect.
If the tank is good it nornally looks like new inside.
I have never had to do but once but if it is still crudy do it all over again.
I have heard of people using rice too but never tried it myself.