Main drain/waste/vent stack pipes protruding through the roof can get clogged with birdnests, leaves and debris, etc.
If drains get sluggish (or gurgle), it may be from this type of clog or partial clog. Spraying a water hose down it will usually flush anything down that you can't reach and remove by hand, from up on the roof, but if it is really clogged, sometimes a heavy-duty plumber's snake needs to be run down it first.
A toilet gurgling may be from this, or it may be from a partial clog in the closet bend (main drain line from the toilet to the stack), in which case the toilet needs to be pulled and the line snaked.
Mike