(See non-toxic cleaners in the last paragraph, and Do Rust Cleaners Work?)
RUST ON RUGS
There has always been one basic chemical available for getting rust off about anything and that was Oxalic Acid. That was the active ingredient in the old petroleum jelly that we used to clean the rust off of all our old chrome car bumpers. The problem is that Oxalic Acid is also known as Lemon Salt. Why is that a problem? Because Oxalic acid can be very corrosive and toxic in strong doses, and a bottle of crystals is a very large dose. Now with a great name like Lemon Salt, wouldn't you want to try it on a steak? Don't try that! It became harder and harder to locate this stuff until finally it is now only commonly available at the drug store, and often behind the prescription counter. When I asked my druggist if there was any other use for this chemical that justified it being in the drug store, he said no, just that because of it's name it was too dangerous to sell it without a lecture.
Second problem was that now there were no instructions as to how to mix it for different rust removal projects.
Finally someone put out a product that has several ingredients, including Oxalic Acid, specifically formulated for removing rust, and at this formulation level, it is no longer even corrosive for skin contact. Does it work? You bet it does. It will work on that rug in the trunk of the car, where you left the snow tracks or shovel too long, or on the rust in the sink. Just spray it on, let it sit a bit and rinse it off. If you look at the photo above, the entire carpet had rust marks but in just a couple of minutes I got the top half clean. It is called The Rust Gun. But in 2017, I can't find it on the shelves any more.
There are other rust removal products that have shown up on the market, generally based on Phosphoric Acid, another good metal cleaner. Note that they are all acids, some stronger than others. Test on a hidden corner of the rug -- it might just burn a hole. Use them with caution and rinse well.
HEAVY BROWN STAINS IN A TOILET
Regular cleaning with vinegar, as talked about below, can keep toilets clean without the negative environmental footprint of putting acids down the drain. Both Oxalic Acid and Phosphoric Acid, if poured into a toilet bowl and left for a couple of hours will take off the orange brown stain that develops in toilets below the water line -- but the the most efficient is Hydrochloric acid. The latest version of "Toilet Bowl Cleaner" by Master Plumber is one such hydrochloric acid based product but it is not so easy to find in the stores the last time I looked. An interesting detail is that Muriatic Acid is easy to find in stores (for cleaning masonary and concrete) and it is actually a 31.5% aquatic solution of hydrochloric acid. Use it as a drastic initial cleaner for built up stains, but it can seriously burn your skin, don't breath its fumes, double flush to rince it away and don't use it often. Don't forget to let it soak for an hour to get the most cleaning with the least pollution. Then maintain the clean porcelin with vinegar.
And for the non-toxic treatments...
The non-toxic cleaner to keep that brown urine stain out of the toilet is simple household vinegar, the same stuff you use to clean the calcium out of the hot water kettle. Pour about a cup of vinegar into the toilet and let it sit 20 minutes. Then pour a cup of vinegar into your tea kettle and boil it to clean the kettle -- but now dump that hot vinegar into the toilet. About two minutes later you should be able to scrub out the brown stain with an ordinary toilet brush and a little elbow grease -- but no corrosive acids down the drain.