Flushing out in-hull plastic fuel tank?

[Keyboardman]

So I have the tank empty and dry and can see a brown film on the bottom, most likely old gas turned to varnish? Wondering what would be a good chemical I could use to try to flush it away or, just not worry too much about it. Thanks.

 

[alldodge]

Could use some acetone, but if there is not that much maybe leave it, the filter should catch anything that comes loose