Cleaning toilet vent stack?

My house house two bathrooms. One of the toilets flushes fine, the other always flushes slow.
Sometimes everything will go down in one flush, but often needs extra flushes, a bucket of hot water, or a couple of pushes with a plunger. When it does clear, the water empties quickly out of the bowl with a lot of gurgling noise. I snaked it with a closet auger, but couldn't find any obstructions.
I suspect the vent stack to the roof is clogged. Though not really proof, the vent for the toilet that works has a screen/cap on it. The vent for the problem toilet does not, and it's never been cleaned out.
I'd like to clean it out and install a cap on it . I'm looking for the easiest approach - are there any chemical cleaners that are safe to use down the vent stack?
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There are many opinions about how to do this. Go to Google, then Google Groups, and put your subject line in the search square. You'll get hundreds of approaches. I used hydrocloric acid followed by high pressure water from garden hose with nozzle. Several in this newsgroup would *not* have used acid. Anyway, it worked.
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Actually, I got THOUSANDS of search hits with that approach. The commonest advice was blast it with a hose - but didn't say what to do if the vent is clogged and the hose water backs up out of it.

I suppose if it worked, that's what counts. I was hoping for something a little milder. Bleach or peroxide? Enzyme or bacteria culture? Something like that.
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You need to hone your google skills. Quotations limit the search to specific phrases, otherwise you get every article with the desired individual words *anywhere* in the letters, and in any order. Go to google groups, put "toilet vent stack" in quotes. You will get your letter, plus another thread. Read the whole (other) thread. After that, try entering "vent stack" a space, then the word cleaning, with no quotes. That will yield about 90 answers, many of which are relevant.
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I would run your snake down the vent first, more than likely if it is blocked it is some sort of debris, maybe leaves, dirt, bird nest, wasp nest, etc.
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Bio-Clean down the stack should clear it out. (You will need to do multiple applications to get it clear, then once every six months)
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BIO-CLEAN because SLUDGE IN YOUR PIPES CAN CAUSE DISEASES!
Don't forget to clear out the Organic Material!
Kills harmful bacteria from your drains! Bio-Clean clears your drains of Sludge! Remove the stink from your Septic System! Makes sinks and toilets stop smelling as well!
Bacteria and insects want your water and sewage to live and grow. Don't let them infect your home with disease!
Get Your 2 Lb. Container of Bio-Clean at PipeDoctorUSA.com Today!
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