Ideally by the use of 45 degree fittings or long radius ells with a clean out installed in every change of direction over 45 deg
If the existing sewer line is lower than basement grade (does it go into the basement floor and out of the house?) you can just connect in to the existing drain. By code, sewer lines must have a slope of 1/4 inch per running foot, meaning that raw sewage will run AWAY from the main plumbing stack of the house. If the sewer line is ABOVE the level of the basement plumbing fixtures, you will need to purchase and install a pump check-valve, and tank to install any plumbing below the house sewer line. If you have any questions, contact a licensed plumber to find out the needs of your home.
Most likely a drain has dried out and there is no water in the trap to stop the gas from coming up. Sink, shower, or main floor drain.
By cutting in a cast iron Wye so the flow enters the sewer line (soil pipe) at a right angle
YES !!!!!!!! Minimum 2" P Trap Yes, and it needs a wye not a tee, and it needs to be vented properly.
You hire a plumber to put in a one way sewer drain valve.
Install a one way check valve in the line from the house to the sewer.
Either they are on a separate sewer line and connect to the main sewer line later on or they sewerage is pumped by means of a machine into the main sewer line.
If the toilet and shower are in an upper floor then there is a PVC drain for both that will drain to either the sewer or septic. If there is a vertical piece to this, as there is in my basement, then you actually get some dribbling and running sounds from the water 'falling' down that vertical PVC. I get this same noise from the washing machine on the main floor draining down to the basement.
This is not recommended but obviously with the right amount of money, plumbing is not impossible. But the average person wont be able to afford the necessary changes so the short answer for most of us will be no. The reason for this is because of the sewer lines. The waste from the shower cant go up without the use of a pump.
Frozen sewer out side
Probably not, but where does the water from the sink and shower go and what sewer problems are you having?
there is a blockage in your sewer line