drain pipe?

My drainage system is on a septic system. How do I find out where the drain pipe runs under my slab of concrete. At one end of the house the drain pipe goes down into the concrete. The septic tank is located on the other side of the house (backyard) where it is annually drained though a pvc pipe that comes up though the ground. Can I assume that the drain pipe runs straight under the concrete from the place where it enters into the concrete to the place where it comes up out of the ground in the backyard. Not everything is perfectly in a straight line but there are fixtures like sinks tubs and toilets thoughout the house that have there own drain pipe or share a drain pipe that runs into the concrete that connect to this straight main pipe under the slab or hopefully it is straight and not snaking around under there. Also, doesn't this drain pipe need to be below frostline from the point it starts from the house since it doesn't have the heat from the house. Thanks for all the help.

There is a limit on the number of bends that can be in the thing without a cleanout. ALso, it needs to have a slope to it of 1/4" per foot. This is a guess, but I expect when it exits the house, it would be below the frost level.

It is very probable that the drain line runs in a straight line from the house to the septic tank. It would have required more fittings and more work to make anything but a straight line and would certainly serve no good purpose. The drain may or may not be under the frost line, ideally yes, but since a drain does not contain water like a supply line, and the drain water is moving on its way to the septic tank, unless it get extremely cold, it won't freeze.

Well, it can dip to -30 degrees were I live. Infact I think it is -4 right know outside.

Unless it's a very long away from the house, and it probably isn't, it won't freeze. There is enough heat generated in that septic tank to keep the line from freezing.

It's not written in stone, but quite often you can draw a straight line from your main stack to the septic tank.