You can put a liquid pipe snake down your drain or put a hose down there
You put a drain auger down the pipe from the nearest cleanout. You will feel the blockage when you get to it, - then break it through and clear it with the auger.
To drain the over flow from a tank or fixture
Radio Shack "drain pipe tracer".
The condensation received and goes down the drain pipe enters a pan where over time it evaporates as the water is a trickle and does not over load the pan in most cases
The toilet flange is usually above the floor level. You would have to cut it off the drain pipe and cap it. How you do this depends on what type of pipe the drain is made of. Even if the drain should be below the floor level, you have to seal the drain or sewer gas will come up from the drain.
Foul Air
Yes, a sewage drain pipe can be too large.
If you are talking about a roof water drain pipe to sewer it is illegal. If you are talking about a sink drain pipe well that is where they all connect to so yea.
dvw pipe = drain, waste and vent pipe.
As long as the pipe going into the wall is straight, the rest of the drain pipe can be routed however it needs to be. Very often the trap is at an angle to the pipe in the wall.
You want the drain pipe for a kitchen sink at least 18" above the floor. You do not want it any closer or it might be kicked, or damaged during building or installing the faucet pieces.