Removing Rust from the Standard Exhaust

[Ebme Geek]

You can get Phosphoric Acid quite easy, "Ph Down" you can get in an 81% variant. Get off as much rust as you can with wire brush attachments first, but as said you may make holes, I have used Kurust on other things but not on exhausts but would give it a bash, I am sure it's active ingrediant is Phosphoric Acid but there is mention of it having a co-polymer element to it as well.
Overall biggest advise get off as much rust as you can mechanically, rather than rely on liquids, they only seem to go so deep.

I have just bought stainless direct from Motad, I had holes  :\