Most varnish and build-up created from sitting for long periods may be flushed through the drain in the bottom of the carburetor bowl using clean, fresh gas.
Unless rust has formed inside the tank.
A succession of disposable fuel filters, or one that is cleanable is probably the easiest fix to remove debris.
It is better to Not fill the tank for a while, until you have made a whole bunch of short runs adding fresh gas each time.
( ten- fifteen miles or so, whatever works )
A fuel conditioner would be helpful to remove varnish.
You did not say which state dmv is particularly abusive.
Best thing to do is object at the time they demand some high price for their value-less services.
The art of taxation may be compared to plucking feathers from a goose when you want a feather pillow.
You want to do it with the least amount of hissing, squawking, and snapping.
Complain to a supervisor at the dmv. Tell them the scooter is Not worth this much !
They function from standard value tables and what you tell them regarding the sale.
redk