Gas tank cleaning

[Argent]

I drained the tank, and pulled it off my bike.  

Some guy at work recommended filling the tank with kerosene and letting it soak for a week.  Sounds odd to me, and thoughts?

Also, the inside of the tank looks like it has some kind of coating; but it's not uniformly applied.  It fades off the farther you get from the fill hole.  
The pictures aren't very good, but you can kinda see the texture.  The coating is hard to the touch, and looks kind of like a brown rhino liner.

In one of the pictures you can see a "line" of this coating, it's attached to two parts of the tank and extends between.

Is this stuff stock?  Or did some previous owner spray some crap into my tank?  

Is it anything I need to be wary off?  I don't need rhino liner floating into my carbs.

   Thanks!

[18Bravo]

Whatever's going in there, I'd just run an inline fuel filter between the tank and the carb. I do this anyway on builds. For general cleaning, there's a good sticky at the top of the project forum on hondatwins.net.

[TOOLS1]

It looks like it might be (Caswell http://www.caswellplating.com/epoxy-gas-tank-sealer.html ) tank sealer. I would not worry about it. If you want to clean the tank, vinegar does a good job. Just fill it with vinegar and let it sit a day or two, and then rinse it out.
TOOLS

[shinyribs]

Caswell dries clear. Kreem is brownish colored. The texture doesn't ressemble anything, though. Odd, for sure.  

Kerosene wont clean anything unless you are trying to dissolve some sort of petroleum varnish that has accumulated. Vinegar cleans everything. But if that is some sort of liner in there, I don't know how it might react to vinegar. Possible it won't react at all.

If you swish gas around in there does it come out clean? If so, inline fuel filter and rock on. JMO

[beemerboy]

If you use vinegar and are left with clean bare metal in the tank, you have to do something immediately. Left uncoated, the bare metal will flash rust in literally, a minute. Having rinsed the vinegar out, flush with a little baking soda in warm water. rinse with fresh water again. Then, as soon as possible spray fogging oil into the tank, covering all the surfaces. Now the tank can sit empty for a while.

[LukeM]

For my new little cutie (CB175), I tried a gallon of Evap-O-Rust.  It was around $22 at O'Reilly's Auto Parts.
I loaded the tank, and rotated it about every 2-3 hours so every side was exposed to the liquid.

After 24 hours, I dumped the Evap-O-Rust out, and with it came a bunch of black crud.  I rinsed the tank out 2-3 times, and then fogged it with some 2-stroke oil.  It works very well, and didn't harm the paint when some drooled out during the agitation.  I use a clear fuel line, and there are a few bits of grit still in the tank, but that's what the inline fuel filter is for.

It's also reusable, so I can de-rust the lawn furniture with it if I wish.  My other option was to use vinegar or some other preparation.

One more data point.
Luke M