Chainsaw Repair

Put a bunch of nuts etc and shake around with a cleaner of some type.

Red kote I hear works good for sealing etc after cleaned up.   

https://youtu.be/qWmKG-OGT20

A small bit of rust in the tank will rarely cause problems if you don't let the rust get scaly. A small inline filter is usually enough. I wouldn't worry about it once you clean it mechanically as has been suggested.

Only use a chemical tank sealing system if you are willing to follow the instructions to the letter. I have seen way too many people take short cuts and the resulting mess is almost impossible to correct. Failed tank liner will clog lines and orifices with a vengeance and you will not be able to dislodge it to save your life. I've tossed bucket loads of Mikuni and Hitachi carbs clogged full of that gunk that was not applied properly. Stoddard solvent, carb cleaner, paint thinner and ultrasonic cleaners are helpless against that stuff if it isn't applied and cured properly.   

 I've used CLR ( calcium , lime , rust ) cleaner with excellent results. Also  I've used plain white vinegar with the same results. Either one can be put down the drain with no problems when done. 

                           Chris