How to clean rust from inside a plastic bottle, coolent reservoir of a Vauxhall corsa?

Its coolent reservoir of M reg Vauxhall corsa, and it has rust inside, Is there anything which can clean rust from inside a plastic bottle.

I just got done doing the same thing to a Montero overflow bottle. I didn’t have a bottle brush so I used a heavy paper towel and wrapped/taped it around a screwdriver. I took the bottle off the car and put some dish washing soap and warm water in it the used the towel/screwdriver like a bottle brush and scrubbed the insides of the bottle. Took a little bit of time but i eventually got it perfectly clean. Rinse and repeat. A bottle brush would probably make the job easier though.