how to clean out very old gasoline from a tank

Hello Gents,
I recently acquired a 2002 Honda 919. It's got low miles and is in great shape but it sat for a very very long time with gas in the tank.

What do?

Here's a picture of the disaster. The clear spot you see is where I pushed the congealed gunk aside. I don't believe there is any rust in it. Just a lot of evaporated gas.
I've always used a few cans of carb cleanner and two hand fulls small rocks. Shake it all around dump it out and do it over again till its cleaned up the wash out with gas a few times. I'm sure you can find something to pore in there insted of spraying a can of carb cleaner into the tank. And the rocks are just to slide around and help cut all the crud alose.
I don't want to put anything in the tank that will potentially scratch/dent the inside or get stuck inside. I'd use ball berrings but again, it's not rust.
I have used a few methods here and there over the years, but I think what I would do now is take it to a radiator repair shop and see if they can clean it. Think maybe they steam it out? Whatever they do it works well. A buddy of mine plays with old tractors quite a bit and this is what he does now, and the rad shop always gets the tank spotless on the inside.
+1 . . . . a rad shop will be able to get it sqeecky clean toot sweet
Vinegar. Soak for two days, change. Soak for two more days. Slosh it around every few hours or twice a day. Leave on side, turn upside down. Finish.
i didn't say use big pointy rocks. And I use rocks because I have them on hand, i don't have ball berrings.
I don't know if there is a best way. If it were my old bike and wanted to keep the paint and inside tank coating, I would start with something relatively safe that can dissolve the gasoline residue such as mineral spirits (i.e. environmentally friendly paint thinner); next, try some VM& Painters Naptha; next up would be regular gas and aviation fuel; next... pine sol cut 50% with water. If that didn't work, then straight pine sol - which would probably strip any tank coating. Lastly, use some superclean - which will remove any and all coatings inside the tank along with the old gas sludge.
JAB Unsprung Weight Supporter

+1 on the Pine-Sol 50/50. Had good luck using with carburetors, so might be worth a go on a tank. Same sort of mung. Let it soak a few days, shake it around every so often. Good luck.
I have had good luck cleaning old gas tanks with very hot water with dish washing liquid and a tube of BB's. Pour the water soap in the tank add the BB's and shake, replace the hot water and soap from time to time and most of the curd will come out. Rinse with clear hot water and let dry.
Um, not trying to be too smart, but why not just use gas?
As solvents go it's pretty harsh, in ready supply, and should have the same stuff as whats in there. Even @3.50 p/gal it's about the cheapest out there. Plus the tank is made for it.

You can get a decent kit of bottle brushes at HF that could help out without being too harsh.

If you use a hand full of screws and bolts, you can easily fish them out with magnet.
I've cleaned/sealed dozens of gas tanks. I use a strong detergent (any kind will do)
with hot water. If there are heavy deposits, I use a small immersion heater:
http://tinyurl.com/d9yvn2u
Acetone...........cleaned a inboard boat tank with "gas" that had been in the tank for 12 years........the sludge was 1/2 thick on the bottom. Acetone melts the sludge. Soak type carb cleaner (stinky stuff that comes with a nylon basket but it destroys paint), one drop on the paint can lift the paint in seconds (rap the tank in cling plastic rap), Rad shop will work too.
Skip the mineral spirits, naptha they don,t work on the tough sludge.
Not good; acetone is extremely flammable, pricey, melts brain cells... Any detergent will
remove old gasoline sludge.
+1 on this. safe and effective.
def Ginger th wonder dog

Remove the tank and remove the fittings. Fill the tank with hot water and Super Clean, a very strong alkaline industrial cleaner. Wear gloves to protect your skin, Super Clean loves protein and will dry your skin uncomfortably. Agitate the tank.
Repeat as needed.

Super Clean is available at Wal-Mart and auto-parts stores. It is water soluable and will leave your tank very clean. I would follow with fresh fuel and a bit of Techron.

While you're at it, the remaining Super Clean will remove grease and oil from your driveway.
Lots of good suggestions. I think I'll call a few radiator shops and see what they can do. If not that, then I'll go the hot water and mild soap route, followed by gas.
I don't want to put anything but liquid in the tank, and I don't want to strip it's coating.

Thanks for the advice guys.
Have you tried taking a pressure washer wand to it?
If it is flaking off, get some flakes out of it and just see what dissolves them easily. As mentioned it might just be gasoline.
Another great idea. Thanks.
Radiator shop, vinegar, or trisodium phosphate. You can buy TSP at any hardware stores. It's the detergent additive that they removed from laundry detergent, but in the 70's it really got whites white. It does great on any kind of petrol based stuff.
I used it on the tank of a 54 Ford that had been sitting for a dozen years.
Wish I'd thought of a radiator shop. Time:money is right with the rad shop, but if you're a DIY guy, it's hard to beat vinegar (for rust and scale) or TSP for petroleum based removal.