All of the above tips are excellent. Once you have taken the acetone out, if you find out it still has goo in it, this is what I did with the gas tank from my 54. Sorry if its a bit long, but this really worked well.
My 54 was parked in 1966 and I cleaned the tank with this process about two years ago. It had a lot of brown dried up stuff in it. None of it stuck to a magnet so I knew it was old dried up gas. Was probably parked with a full tank, and when I got it, it was a real mess inside.
Vacuumed out as much loose stuff as I could. Put in a half cup of LYE and filled the tank with water. I wore gloves, and safety goggles as this mix can eat your skin. Keep a garden hose handy and rinse off anything you don't want the lye/water mix on. Do all of this outside. I let it sit overnight the first time. Could swear I could hear it boiling inside. I did not apply any heat.
I dumped it out, it was very brown and I did this two more times. The third time the water/lye came out very clear. Rinse the tank out with the garden hose a fair bit. You could fill it and drain it a couple times. After drying it out in the sun for a few hours, I vacuumed it out AGAIN, blew compressed air in there and then rinsed it with a little gas, then dumped it out. For the next year (about a dozen tanks of fuel) I used a big fuel filter (Hastings GF115) before my fuel pump. This filter is actually for fuel injected Fords and has a much finer material than a carb filter.
Last summer I removed the big filter and just used the factory sediment filter on the fuel pump. It took a full year of use (probably 4000 miles) before that filter needed to be serviced a few weeks ago.
Hope this helps you and anyone else with a dirty fuel tank. The local rad shop won't clean fuel tanks anymore so I had to do this. Very happy with the results.