Justin, there's a few things to consider when it comes to scoring WVO. Here's my take. First off, you need to avoid hydrogenated and partially hydrogenated oils. They're bad- thick, nasty, fatty goop that doesn't lend itself well to any part of this process from the fryer to your tank.
Go in and eat somewhere, and then ask to talk to the manager or kitchen manager and very politely express your interest in assuming the collection of their waste grease. Try to get the kitchen manager to show you the box that the oil that they use comes in. If it says non-hydrogenated on it, use it. McDonald's is not a good place to start. Look for an independent establishment. Go round back and discreetly check out their oil trap, and see if it's covered and shut. I used to rule places out just by seeing how gnarly their methods of disposal are. The more **** floating in it- paper towels, gloves, dead rats, I've seen it all, but don't worry about the french fries or egg rolls
- and lots of water mixed in with it in it means WAY more work getting it to a usable state and results in less junk after settling and filtering. Also, remember- in many cases, if you are replacing the contracted services of their previous renderer, that means if you take any of their grease, you'll probably have to take it all. Which means you have to consider disposal of the worthless crud. I prefer to dump it guerrilla-style back into unlocked grease traps
. You can convince them to pour it back into the 5 gallon jugs that it comes in and you can collect it that way and they won't necessarily have to end their contract with their renderer.
In my experiences, Asian joints have the best grease, hands down. They fry a lot of food, use quality oil, and change it out frequently. Mexican restaurants can be good, as well as down-home fryer-heavy kinds of American fare.
Here's some tips from the collective wisdom about collecting WVO.
http://www.lovecraftbiofuels.com/index.php?option=com_content&task=blogcategory&id=4&Itemid=76
http://www.greasecar.com/article.cfm?aid=19
Remember, you may need to travel a bit further to secure sources of WVO, but it can be worth it, within reason.