Toilets don't flush properly

Hi, I have 3 bathrooms in my house one in the basement and two on upper floors. Just the basement one empties with force. The upper two are on emply slowly, no downward vacuum.
My question is this: can the venting be casusing this problem. If so is it possible to check this without going up on the roof. My house has a terra cotta tile roof and 14/12 pitch. The tiles are just plopped on the roof so walking on this surface is asking for disaster. Any informed suggestions?
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Same questions that always need to be asked. Do they flush better if you have to do a secondflush? If you pour water from a 5 gallon bucket, does the toilet take the water quickly and well? Are there any of those 'disinfectant' products in the tank or bowl? Remember, I mentioned http://www.toiletology.com/blue-goo.shtml in a post recently in which you mentioned the elongated throne. There are suggestions, besides regarding the blue-goo, in the FAQ section, at http://www.toiletology.com/frequent.shtml of the Toiletology 101 site.

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Are they all the same make and model? Have they changed or have they always been this way? How old are they?
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Joseph E. Meehan

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