Double-clicking on a slider, or clicking it while holding the Ctrl-button, instantly resets the slider to its default setting. Additionally, clicking and holding anywhere on the slider outside the knob will animate the slider to the new position.
If you have a Mac notebook with a trackpad with Multi-Touch gesture support, you can also reset sliders by simply swiping three fingers to the left or right while pointing at the slider. Swiping three fingers up/down will maximize (boost) or minimize (kill) the slider.
To reset all sliders at once for one side, you can use the keyboard shortcuts Shift-Alt-A (Deck 1) and Shift-Alt-L (Deck 2).