I don't.

Welcome to owning a Hummer.
"Ex Umbris Venimus"
Sent from my iPhone
Haha thats funny. But for me, this is what i do.
For the plastic stuff, i use a damp washcloth to scrub off the dirt and other gook.
For the seats, well mine are leather, so that cleans up fairly easily with a wipe of some sorts.
For the actual carpet, well i have weather tech floor mats, so i dont usually deal with this problem, but i find that waiting until its dried and then brushing it off works relatively well.
If you have mud on the headliner, im not really sure how to do that, maybe an armorall wipe or something like that.
Hoped this helped some.