1-Clear the obstruction from the vent or drain pipe
2-Be sure the vent is properly sized and graded up towards the penetration of the roof, or where it ties into the vent stack.
Yes.
Who needs a toilet
A toilet has to be vented otherwise you are trying to force liquid against the air in the drain and it is pulling against a vacuum. It will never flush right.
No, that is why it is called a vent pipe not a soil line
Sounds like your washer doesn't have a connection to your "stack pipe". As water moves through a drain pipe, it creates a vacuum behind it, the "stack pipe" or "vent pipe" is usually a pipe that goes through the roof of your house and provides an open air connection to all of your plumbing fixtures so the vacuum is provided a way to suck air rather than sucking the water out of your "P" traps or other fixtures such as your toilet. Chances are your toilet is also "sucking" from your washer, but you just don't notice it. It is also dangerous because if the washer or other fixtures are sucking water out of your "P" traps, then you may be getting methane and other sewer gases into your house. Have a pipe run from washer drain to your vent pipe and this should eliminate the problem. Be sure it connects to the vent pipe because if you ever have a sewer backup, the vent system won't allow the gray water to empty into your house through the air pipe.
Yes if the vent pipe is 4" and vertical by code and there is nothing connected between your toilet tee and where you would connect your new toilet tee. If not worried about codes then yes you can connect to a 3" vent line if no other vent lines are connected down stream. If you have a vent pipe that is less then 3" and or you have other vents connected between your old toilet tee and your new toilet tee then NO you can not connect a new tee for your toilet.
Look at where the cold air is coming from and see if it can be stopped, if not insulate the pipe.
Any vent is usually the size of the drain or waste pipe it is connected to. 3 or 4 inch on a toilet.
No, it has to be vented
No I just checked and mine has no condensation, thanks fro asking
The highest 4 inch pipe should have a vent on it, or directly above a toilet junction Above the flood level rim of the fixture it is servicing IT does not mean the toilet
Check your vent pipe. Does it vent to the outside? If so, is it blocked? Is the vent pipe breached? The vent is the most likely cause.