NOTE: Older toilets used the force from a greater volume of water to remove waste, while newer toilets require adequate venting to remove waste.
The following symptoms are signs of a clogged waste stack or vent pipe:
Water rising in the toilet bowl
Slow flush (bowl water rises quickly, but falls slowly)
Frequent clogs
Having to hold the handle down to get a proper flush
Sounds coming from other drains in the area when the toilet is flushed
Bubbles coming from the trapway opening during the flush