Good answer, Gandalf; also, be sure (on most boards) NOT to route your individual drum tracks to a submix bus AND the Stereo bus - if you do, you'll have your drum submix going to the mixer output TWO ways, which will make it louder as well as having two differently processed versions of the same thing showing up at the output - this can/will cause phase cancellations, etc, making things pretty muddy/crappy sounding (not to mention confusing - "I just turned down the drum submix, but it's still too loud in the monitors - WTF??!?")
IOW, if you're gonna use a submix for drums, vox, whatever - send the individual tracks ONLY to that sub (Sub 1, left, Sub 2, right for example) and then, in your MASTER section of the board assign Sub 1 and Sub 2 to Left and Right Stereo mix ONLY.
Also, be sure to ONLY assign any processor outputs used for your submix to ONLY that submix - otherwise, you'll get "phantom" reverb in your main mix that might be louder than your actual tracks - this means you'll need a SEPARATE reverb for subs. One way around that problem would be to keep the individual tracks in your sub mix DRY, and only assign the BUS OUT to your main (or only) reverb unit's input, returning the output of that 'verb to STEREO MIX.
HTH... Steve