You can use Eco-Complete all on it's own with no problem. It's kinda expensive though and really only worth it if you have plants.
Some people use a layer of soil and then gravel on top, but I don't know how easy that is to do. And again, not worth it unless you are interested in growing plants.
If you want a dark substrate that isn't gravel, look into black tahitian moon sand. I have some in my 10 gallon and really love it.
To clean it, you would use a regular gravel vaccum such as the Python or any brand gravel vaccum.