Since replacing the old toilet with a new water efficient high rise toilet the venting does not work. The vent is under the sink and worked fine prior. The toilet doesn't flush properly and gurgles sometimes in the utility sink in the laundry room at the opposite end of the house. The toilet works fine when the old self vent was removed. Tried putting on two vents. Did not work. Drilled holes in old self vent and it did work better. Does the new toilet require special venting? We live on a farm with a septic tank and our own well.

Yes you have a blocked vent. The first thing I would do is replace the AAV under the bathroom sink. Get back to me with the results. Good luck, Tom

Tom,
Changed vent to 1 1/2" MIP threaded ABS trap vent. The toilet would not flush but eventually the water went down to normal. Took the vent off and the toilet flushes just fine. Any other suggestions?
Thanks,
Cece

Took the vent off and the toilet flushes just fine.You have just told me that whatever you're using for a vent is faulty.

Changed vent to 1 1/2" MIP threaded ABS trap vent. I don't understand your setup or what you're trying to tell me.
Let's start over.
You do not have a roof vent, correct? You have a AAV just after the trap that looks like this (see image). Correct? If this is so why are you complicating a simple problem? Either replace the existing vent with a AAV or run a vent to the roof. Good luck. Tom

We had new siding added last summer and the outside vent pipe removed at that time. The picture you posted looks just like what we have and we did buy a new vent to replace a possibly faulty vent that we never had trouble with until we put a new higher seated toilet. Could there be any other solution other than running the vent pipe up the outside wall? I appreciate your time and efforts. Wishing now we would have just kept the old toilet!