Remove as much water from the bowl as you can. Add one cup of baking soda, followed by two cups of white vinegar (heated, but not boiling). The fizzing action scrubs the pipes chemically without heat stress. Flush with warm water after 30 minutes.
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Here is the breakdown of the aftermath:
Squirt a generous amount of dish soap (half a cup) into the bowl. Let it sit for 20 minutes. The soap sinks and lubricates the pipe. Then, pour a bucket of warm (not boiling) water from waist height. The pressure and lubrication often break the clog instantly. Remove as much water from the bowl as you can