I'll give a quick description of my keybindings and what I did.

My tank really just uses a few keys:

F1 - Death and Decay
1 - Tanking castsequence with rune strike - alternate key alt+2/ctrl+alt+2 (so it keeps rotating while im spamming DPS on my shaman)
v - bone shield
alt+f1 - icebound fortitude
ctrl+f1 - taunt (dark command I think)
shift+4 - unholy blight

Those are really the only keys I use regularly on my DK, and realistically I mostly just use "1" and "v"

For DPS my shamans use the following keys:

2 - just casts lightning bolt
ctrl+2 - just casts chain lightning
ctrl+alt+2 - just casts lava burst
alt+2 - castrandom Lava Burst,LB,CL,Purge
shift+c - all 4 cast flameshock
` - use all trinkets, elemental mastery, etc
ctrl+alt+1 - bloodlust rotation

I also have various heal macros such as:

3 - all 4 shamans lesser healing wave tank's target if friendly, or tank if target is not friendly
alt+3 - all 4 shamans lesser healing wave themselves
ctrl+3 - each shaman chain heals the next shaman in line or themselves if the next shaman is dead or doesn't exist

But for this purpose we only care about DPS. So, I basically did the following:

Ran at boss with DK (boneshield preloaded), drop death and decay just in front of DK so boss would be inside while fighting
Start spamming the "1" key to begin DK rotation
Hit shift+c on shamans to cast flameshock immediately after hitting "1"
Spam ctrl+alt+2 until my shamans all start to cast lava burst (meanwhile ctrl+alt+2 keeps my tanking rotation going)
Spam ` until trinkets fire off, and then spam ctrl+alt+1 until I get the bloodlust buff (takes 1/2 a second at most)

This is pretty much every boss fight. At this point I typically just spam alt+2 the rest of the fight which does the /castrandom, and keeps the tanking rotation going, however on the fight with the dps above I did:

spam "1" + "2" to keep tanking rotation going AND fire strictly lightning bolts, until 4 LBs had gone off
spam ctrl+alt+2 until lava burst x4 begins casting
spam "1" + "2" again until a couple more LBs had gone off and I knew FS was about to run out
spam shift+c until 4x flameshocks went off
spam ctrl+alt+2 until lava burst x4 begins casting
spam "1" + "2" until boss was dead

So the short answer to your question was, I did a manual rotation, not a castsequence