Step One
Go to City / County building permit office and obtain a copy of the relevant code for your area. This is to keep you out of hot water for insurance issues and utility co snooping.
Review the code. Any questions, ask here for advice.
Go to hardware store. Grab a hunk of 1" conduit fitting. Can you force four 6 gauge wires through it? No sense in fighting it. Make it too tight and you'll be using Pull Ells instead of cementing sweeps. Buy a tube of yellow snot for wire pulling lube.
Use chinese finger knots to attach yanking twine to wire bundle. Soften wire ends by wruuuuuuuuu