By plumbing codes, no.
If you have a clogged drain and you have coke in your house .. 1st Poured coke in the toilet than You wait 15 Minutes and Flush the Toilet and After that open The Toilet top part and it will look clean..
The trap is built into the toilet itself, you shouldn't put one in the drain.
The drain is getting plugged and the toilet is lower than the washing machine drain so it is easier for the water to come up in the toilet than to go straight out the drain. Put some drain cleaner down the drain where the washing machine drains and that may solve the problem.
You find an entry point and put an auger or drain snake into it. The entry point can be where a toilet sits on the floor (remove the toilet) or any "Y" point in a pipe that has a plug screwed into it.
If you reduce the soil connection to 2" and install a trap
Usually toilet flange is glued down onto plastic drain pipe. There is a toilet flange that can be glued inside of plastic drain pipe also.
Yes as long as the drain has a trap and is vented
Someone called Peter Toiletie created the toilet and flushed himself down it. He forgot to put a drain in and got squished to death.
Ohpra's Elbow
Yes.
In order to hold water in the toilet bowl (and prevent unpleasant smells from coming into the bathroom) there is an elbow in the toilet. After you see the water go down the toilet, it then travels upwards through the elbow and then back down again into the drain line. The toilet clogs when things are too big to travel freely through the elbow.