manhole blocked

hi there, i might have stupid questions that most of you might think. I'm a woman who doesn't know about plumbing works but a worrier. i think my main sewer has been clogged and i would like to know that

when the drain in a bathtub is slowly draining and some water still remains in the tub and slowly going down , are there any chances that the sewage water from the manhole is contaminating somehow back up in the bathtub?
After i use the toilet and when i flush the water rises up high before it slowly goes down. Is that clean water mixing with the waste from myself (not the waste water from the manhole underground coming backup) right?
are there any chances that when there is a clogging from the main sewage and the water that is left in a toilet bowl (before using toilet and before flushing) is contaminated from sewage water from the manhole somehow?

1) Nope. You likely have a clog in the tub's drain or drain line...collection of hair, body grease, moisturizer and conditioner oils, soap scum, etc. This can be right at the drain or in the entire pipe. - 2) Yep, that's clean toilet tank water mixing with dirty bowl water and the toilet itself is working fine and you can still drink the tank water. Butt, the pipe the toilet's connected to could be blocked where it meets the toilet or further down the line. - 3) Yep, but it sounds like its from the femalehole.

- You need a Plumber or a Drain Cleaning company is all. Since the tub's affected they would (or should) run a Drain Auger through your tub's overflow to remove the clogs and get everything back to new. However, due to so much time (possibly) going by with very slow running drains, they may have to temporarily remove the toilet to remove build-up under it...maybe even chiseling the plumbing pipe back to full diameter.