First, you need to get that wad of string out. A 1/4" snake *should* get past it...alternately, you could use a vacuum on one one end (sucking) and a vacuum (blowing) on the other end.
There is NO formula for this..trial and error/skill and luck, etc. It is a royal PITA. WHo knows what else is in there? A family of mice, rats, bottles and cans, a wad of ice, etc.
After clearing the pipe of what you know you put in it (string, rope, sweat and tears, every four letter word known to man)..you need to make SURE it's clear. Pull a 1/4" or 3/8" rope through (attached to string).
Ater getting the rope out, attach a mandrel (See links at bottom) to that rope, with your actual pulling rope attached to the other end of the mandrel(properly sized). This will clear all the debris (rats nests, concrete, etc) out of the pipe.
Now you can actual start pulling in your cable.
Mandrels & brushes:
http://www.mygreenlee.com/products/det.cfm?id=5183&upc=39255 http://www.mygreenlee.com/products/det.cfm?id=5176&upc=39284 A set of radios will make this task infinitly more palatable.
I can't imagine doing a 450' pull with only 2 ppl - both will be quickly wiped out from material handeling alone. What size wire is going in here? 350, 400?
Good luck.
