Have a ty250 yamaha,was wondering the best way to clean rust out of tank

take the tank off the bike and empty it then fill it with a dozen or so new nuts and bolts.. shake and shake and shake

wash it out with petrol/diesel and then get some of that white petrol tank sealant from the shop in Leeds pour it in the tank swirl it around and leave for 4 days

the sealant dries rock hard and white which has the bonus of been able to see clearly how much fuel you have left

Lazy man method:

A couple big hands-full of nuts, bolts and washers (old or new); wrap it up in a couple old blankets and a bunch of rope; put it in the clothes dryer and let it rip for about 30 minutes.

Have a cold beer.

You might want to wait until the missus will be out for awhile.