Lime & Rust Cleaner

[repoman2000]

This is more a question about cleaning in the bathroom than the kitchen, but it can be helpful in the kitchen, as well...

We have MAJOR Lime & Rust buildup in the tank of our toilet. It is so bad, I could probably take a putty knife & scrape most of it off; it flakes off in chunks, sometimes...

Any tips on how to take care of this? In most instances, I think some CLR would take care of it, but I am worried about the harsh chemicals eating & destroying the plastic parts that control the flushing mechanisms. Plus, It may not work at all, when it dilutes in the water... I don't know. Our landlord would get mad if we melted our toilet.

Suggestions?