This a quickie, but a really handy one because it lets you drag out the brush to the exact size you want (I usually make the brush just a little larger than the spot, spec or object I want to remove). Here’s how you do it:
You hold the Option-Command keys (PC: Alt-Ctrl) then click and drag out the brush right over the spot or spec you want to remove. See the video below.
NOTE: No Audio
Hope you found that helpful. 
Have a good one!
-Scott
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