How do i go about locating the sewer clean out?

OF course some homes don't have them, ( older) but there should be a large cap or pipe with a plug that screws out about 4 inches round.

It may be between the house and the street were it meets the sewer, some are under the house or basement.

If not, you can run a line though the vent pipe coming out of the ceiling, or even take a toilet up and run a line though the pipe under the toilet

First you have to know where the city sewer service is located, some are in the street and some cities have alley ways for their services such as sewer, water gas and electric service. You can find this out by calling the city sewer service in the phone book. After you have found this out then you can do as Sr_Chuck says and look for the clean out around your house. It should be within three foot of the exterior of your house, if it is a somewhat new house it will be as he described, maybe a white plastic about 4 inches in diameter. If you have a bathroom either on the front side or the back side of the house, the same side as the city sewer is on, that will give you a clue. Most times your sewer will come straight out from the wall that the commode sits on in the house. De depth of your sewer line can be as little as two feet and as much as the depth of your basement if you have one.