Large burping bubbles from toilet when flushed
Hello everyone, I have a rental property I have been working on and have a problem with the toilet. When the fella who was living there moved out he said that the toilet was not flushing properly, he was right. It would swirl very weakly and every now and then it would barely flush all the way. It was old and ugly so I opted to just get a new one. I bought a good brand name, glazed trapway toilet and installed it. Everything goes down fairly decent but as soon as you hit that flush lever a large bubble bursts up and sometimes splashed up on the seat. The air seems to come from the small hole at the bottom on the front side.
I recently had the clay pipe main line cleaned out and can stick a garden hose into the clean out in the yard and push it to the point to where it should be reaching the sewer. I got up on the roof and stuck the hose in the vent and can see it go past the main line clean out in the front yard. Everything seems to be unobstructed, even the pipe under the toilet is clear. Even though everything seems to go down fairly decent could there be something between the main line and the pipe under the toilet (the part you can't see)?
Any suggestions? Bad toilet maybe?
It may not matter but before I took off the original toilet I replaced the water supply valve behind the toilet, it was bad but didn't help the initial problem very much.
Thanks in advance.
Scott