how to check if a 2" vent pipe is plugged?

I suspect I have a plugged or clogged up vent pipe, because sewage smell is coming out of the toilet.
I have tried snaking, vacuuming, hosing the vent pipe from the attic (cut the vent pipe there to avoid going on the roof) to no avail.
The odor is so annoying, I'm ready to hire a plumber or cut open a wall and the vent pipe to fix the problem. But whichever way, I need to be able to tell if the vent is really plugged before the fix, and to verify it is not plugged after the fix.
Are there ways to see if a vent pipe is plugged? I know it's not completely plugged up because when I attach a vacuum at the attic, the toilet water get sucked into the drain. However, when I stick a snake down from the attic, I never can make it come out from the bottom at the crawl space. I believe there are several 90 degree turns, such that when a stiffer snake is used, it is too stiff to make the turns.
I called some plumbers and ask them if they have camera they can stick into the vent pipe (2-inch diameter), and the answers are no, the cameras only fit drainage pipes. Surely someone must have thought of the need to examine a vent pipe?
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peter wrote:

Are you aware that the smell may be nothing more than a failed wax ring? While a blocked vent may be a cause, there are many other possible causes. A cracked toilet is yet another.
--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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I will check the ring. Sometimes flushing the toilet causes a large bubble to come out of the toilet. That is not normal. That's why I suspect the vent is clogged.
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peter wrote:

Agreeing with Joseph; you're on the wrong track. The water in the toilet bowl seals out any sewer gas....unless the wax seal is defective (likely) or there is a flaw in the bowl.
Jim
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What about cleaning the toilet more often?
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