I emphatically disagree,, Rebel is notorious for rusted fuel tank..
I understand the intention to test with unrestricted fuel flow, but one does so at the peril of clogging carburetor with contamination..
I understand that, but the petcock has it's own filter. I wasn't suggesting running it for any length of time without a filter.
If the tank is badly rusted, it will need to be derusted. There are a lot of expensive chemicals out there for that purpose. For severe rust, I have always used undiluted muriatic acid. For a tank as small as the Rebel's, get enough to fill the tank. Remove the tank, place it where it is supported well, remove the petcock and plug the opening with something made of either strong plastic or steel. Muriatic acid will dissolve aluminum.
Before using acid, you have to get anything oily out of the tank, or it will act as a barrier between the rust and the acid. You can get some stuff called SuperClean at Wallyworld, also Home Depot has pretty much the same thing under a different brand. Be careful with this stuff. It will take the skin right off your hands. Wear rubber gloves while using it.
After washing out the tank with this stuff (pour in a gallon, slosh the tank around, then repeat several times) finally hose out the tank with a water hose till there is nothing left in it but water. Pour out all the water, and let the tank thoroughly dry before pouring in the acid. Muriatic acid has a strong reaction with rust, pour it in slowly, and keep your eyes covered. It may seem like it is boiling, which is normal. It is destroying the rust. Let it set about 24 hours, then pour it out, and again rinse out the tank with water. There should be no rust in it. Then pour in a qt. of oil and slosh it around until the whole inside of the tank is coated, to protect the tank from rerusting. Pour out the excess oil. It is not necessary to get all the oil out before putting gas in it.
I've never tried using nuts and bolts or pieces of chain to clean a tank. The reason is because of how much trouble I've had manually removing rust from exterior surfaces. You just about have to grind it off.
There are other rust removal chemicals out there, but muriatic acid is the cheapest and strongest. A couple of decades ago, I soaked most of a VW bug in it, a piece at the time. It worked wonders. If you use another chemical, the same prep work is still necessary. There must be nothing oily in the tank.