Dirty rust flim has started collecting in bottom of toilet bowl what is it and how do you get rid of it?

Sounds like you have a maintenance problem that some elbow grease and a few cleaning chores would cure. Get some "works" and use it on the toilet, use a brush, do this every few days to keep it clean, put some "tidy bowl" or some other drop in, into the back of the toilet.

As for the "plug ups" put some commercial "Plumbers helper" either the sudsy kind or the regular kind from Home Depot. Follow directions and use it every few months or as much as needed.

Have someone check your air vent from your lines on the roof, it may be plugged. You can run a snake or even a garden hose down it to unplug it.

well water or city water,the 2 are not related,email if moreQ's