Fuel tank restoration

I have a couple of 6 gallon fuel tanks that I use for transfering fuel from the gas station and auxiliary usage (I have a 12 gallon built-in), I decided to paint them as they were looking "ratty". Tremclad "Fire Red" is a good match and I found a source for the decals https://www.outboarddecals.com/store/c/110-Mercury-Fuel-Decals.aspx I'm going to put Mercury Marine (1975 era) on one side and Kiekhaefer Mercury (circa 1970) on the other.
Tank before painting

Decals

Excellent idea!
I have one very similar from the 80 that is not in use. Any suggestion concerning how to clean them inside?
Mine has old gas + oil.
Thanks!

Just dump the old gas/oil and put fresh gas in it, let it sit then shake it to clean.
Here's the finished tank

pufffff beautiful.
I do have exactly the same tank.
My tank is empty now, I will try with some fresh gas and shakes.
I heard that some people used some sort of acid, that is why I asked to you.
Congratulation on the restore!

The metal they used is plated and I think acid would remove it causing rust. Paint thinner would work. You can carefully remove the fuel connector assembly and clean the pickup.
If you want an ultra retro look you can use the Kiekhaefer decal.

I would usually coat the inside of them as well. To clean them I use E 85 let it sit for a week and dump it. THe e85 is then good for bonfires.

I restored the same tank.
Let the tank dry then add a 12 inch chain and shake and vacuum.
Do that a few times. Then add POR15. It only takes a ounce or
two. Let dry....good to go.
Did my harley that way as well with great results.

It all depends how bad the tank is inside. Worst case is hydrochloric acid bath overnight. Yes, it will damage what's left of the zinc coating inside, but if you take care of it after flushing/cleaning, it will last a lifetime. Yes ethanol is a good cleaner, but never store the tank with it.
After decal placement, I like to clear coat over everything with epoxy. Nason makes a great product, available for a reasonable price at your auto body supply store. Mix 4 to 5 parts clear with 1 part activator. Use up within 12 hours max....(you can extend life by freezing by about a days time). After that it will gel/harden regardless.
Nice job on the tanks, by the way.

ive heard one way of cleaning the inside of a tank is to put a lots of steel nuts inside the tank , attach to you car wheel (off the ground and tumble it for a while , that depends on how bad the tank is. w

Fun idea, I'll try that on my next drive for groceries....I can do 4 tanks at once.
Seriously, neat idea. Make sure you have in 2 wheel drive, no positraction, block tires....cover brakes to keep a slow rotation....unless it's a manual transmission in low gear, which still might rotate too fast...an automatic will run too fast also, unless brakes are applied lightly. Remember, the speed of tire is DOUBLED through differential if other tire is on the ground. This procedure not recommended for the general public, eh?