Toilet location

If I install my basement toilet near (within 4 feet) the lateral drain that leaves my home (not sure if it is 3" or 4" cast iron) do I have to have a seperate vent? The main stack is approximately 15 feet away from the area I would like to place the toilet. the I'm not quite sure what code says about tying in a smaller line to the main line and how venting is affected. Could someone explain what UPC says regarding the matter. I can't seem to find an answer.

A toilet has to have a vent. The main waste stack does not qualify as a vent. You would have to vent the toilet up to the first floor, and tie into the vent stack, above the flood rim of the fixtures on that level