Stay away from fast-food, or any place that uses hydrogenated oil. Its bad for your body, and your bus!
Locally owned restraunts, especially Asian food is the best. Sometimes chain-restraunts will let you take it, but usually the manager is a dick. Little cafe's sometimes have good oil. Italian restruants do too.
Talk to an employee FIRST, sometimes they will say "Go ahead" especially if no manager is around. Talking to the manager can be a bit of a pain at corporate chain restraunts, as they usually are ball-less and afraid to 'break' their contract with the oil collection company.
Heres what I do when Im on the road lookin for oil:
I find a bunch of restraunts all in one area. I drive up one side of the street, and drive behind every restraunt that is a possibility. I get out and look at the oil and decide if its even worth my time.
Then based on that I do the following:
If its too low or way too gross, I leave and go to the next restraunt
If it looks good, and there is a good ammount there I look around and see if Im gonna bother anyone by taking it. If not, I usually just take it. If Im in a particularly good mood that day, or if I see employees comeing out the back, I ask them for the oil, and explain what Im doing. Usually they say go ahead, or they refer me to the manager. Managers of locally owned business almost never say no. If its a chain restraunt, I usually resort to just taking it, if I can do it without anyone noticing.
If the oil is locked up, I go ask an employee, or if i see a cook or someone come out the back I ask them. Im usually refered to the manager, and explain what Im doing. If they say yes, then they pull it out, I inspect it, if its good I take it.
The tricky part is the managers of chain/corporate restraunts like chili's, applebees, etc, etc. They are usually completely ball-less cowards, and/or assholes (just ask the employee's, they'll tell you their manager is a dick!). If their oil isnt locked up, Ive resorted to taking the oil anyways when I was told no, because I was in a hard spot (like stuck in Knoxville all day looking for oil).
If I think Im gonna have a hard time with the manager, I usually put on some nicer clothes and clean up a bit as best I can. Come into the restraunt with a happy face and say some speal about how I recycle vegtiable oil for free, and wont charge. Sometimes this works, othertimes they are still assholes.
I bought my bus in Asheville NC, drove it to virginia beach, and then drove around the country until I got back to California. All together 4000+ miles. I stoped and hundreds of restraunts all along the way. Being given oil, taking oil, and once I took it after I had been told no (knoxville).
All together, stay locally owned if you can. Employees AND managers are friendly. Sometimes you can luck out at hotels that have their own restraunt too.. ALWAYS TALK TO THE EMPLOYEES FIRST!
Ive never had an employee tell me no, or be unfriendly to me. They always think its really cool. Its only when they ahve to ask the manager that you can run into trouble. The cooks and employees coming out the back are real friendly too.
ALWAYS ask if their oil is hydrogenated! If its hydrogenated use something else unless you are in a tough spot. If they dont know if its hydrogenated or not, look in the trash for an old container, or ask to see one, "if it wont be too much of a hassle". After a while you can tell if its hydrogenated just by stucking your finger in it and seeing how thick it is. Hydrogenated oil is usually darker/thicker, but it takes building of the skill to spot it. Again Ive stoped at hundreds of resturants. Id say it took me about 3000 miles until I really got any kind of system or science too this down.
Happy scavanging!... please dont take my oil ;)