See Combination Pistons.
Cylinders which have a flat disk at the bottom which, with their vertical movement, allow marc to be continuously immersed in must
A piston is one of the numbered thumb buttons or toe studs on the console which can memorize a combination of stops. The organist can choose the stops to use by turning them on and then set them on one of the numbered pistons. (Most organ consoles have a Set button on the lower left corner of the bottom manual which is used for this purpose.) Then, the organist can recall those stops at any time by pressing that piston. There are general and divisional pistons.
Buttons located underneath the manuals that are used to control the stops and couplers.