In the following video, a man in Japan has designed a toilet to accommodate his handicap.
Question: What causes a hard crust of grey matter to form on the bottom of my toilet bowls?
A: Not flushing a toilet after every use is one reason scale develops in a toilet bowl. For example, I rented a one bedroom apartment to a woman with an infant. The only bathroom in the apartment opened into the bedroom. In order to not wake the baby, she would not flush the toilet unless absolutely necessary. As the scale began to buildup in the bowl the toilet became more and more tempermental. To add insult to injury, she poured black hair dye into the bowl which turned the grey scale permanently black. The plumber who replaced the toilet said the scale was caused by salts in the urine.
What causes a knocking sound when my toilet flushes?
A: Noises are not always easy to isolate and fix, but I'll try to give you some ideas.
Loose pipes may be knocking against a structural stud or joist. If you can see the pipes below the bathroom, you may be able to cushion them or anchor them with pipe brackets where they touch wood.
High water pressure can be the cause of lots of different types of noises. The desirable household water pressure is about 50 psi. If you have a pressure reducing valve in your system, it may have failed and needs adjusting or replacing. High water pressure also causes the rubber parts inside a toilet refill valve to fail early.
Worn out parts (washer, seal, etc.) inside a refill valve may be the cause and since these parts are usually rather inexpensive, replacing them is the first thing I'd try.
Some houses have builtin air chambers in their water supply system that are meant to cushion the sudden stop in the flow of water. They are in the walls in most cases, so the only thing you can do is hope you have them and that they have become water logged over time. The solution is to turn off your main water supply; open up every faucet in the house to drain all the water from the system. This hopefully restores the air cushions in the chambers if you have them. Add-on water pressure chambers are available to fit a number of different size pipes and a variety of situations such as washing machines.
You suggest the knocks may be clogged water supply line. Galvanized pipes do become restricted with deposits, but that usually means reduced water pressure, and the toilet tank will be slow to refill. I'd try the above before I attempted to replace galvanized pipes.
Here's a link to a good article on plumbing noises:
Question: How do you remove rust stains from a toilet bowl??
A: There are at least two commercial products available in hardware stores for removing rust stains. One is Iron Out of Iron Out, Inc., 1515 Dividend Rd., Fort Wayne, IN 46808-1126. I've had very good results on a number of occasions with this. Another is ZUD Cleanser a product of Boyle-Midway Inc., New York, NY 10017 that I have also used successfully.
A homemade receipe for a cleanser is to sprinkle "cream of tartar" over the stain then cover the cream of tartar with paper towels. Next saturate the paper towel with hydrogen peroxide and allow it to soak.
I found the following in "Formulas, Methods, Tips and Data for Home and Workshop" by Popular Science and Kenneth M. Swezey.
Iron and rust stains that are fresh can usually be wiped off or washed off with household detergent solution. More stubborn fresh stains may be removed with fine pumice powder or mild scouring powder and water. If the stain has gone deeper, sprinkle with sodium hydrosulfite powder (the dye-remover chemical sold with some packaged household dyes), dampen the powder, and leave for not more than half an hour. Follow right away with a solution of sodium citrate. Repeat the sequence, if necessary. Finally, wash with water and dry. This treatment works by changing colored insoluble salts into colorless soluble ones that can be washed away. It may, however, dull polished surfaces somewhat, possibly necessitating repolishing.
I recently learned that using household bleach on rust stains in a toilet bowl "sets" the stain and makes it virtually impossible to remove. I haven´t been able to confirm this.
The Washington Suburban Sanitary Commission has this to offer regarding stains. Green stains on porcelain fixtures are clear evidence of aggressive water and the utility company supplying the water should be consulted. Accumulation of significant amounts of sediment, especially in toilet tanks, is a possible indication of corrosion in either the home plumbing or the utilities primary water distribution system. The color and type of sediment is indicative of the origin of the material.