My house is only about 9 years old and the PVC waste pipe from my second floor master bathroom is leaking, and may have been for some time. This pipe travels from the second floor through my first floor kitchen wall into my crawl space. It is in the crawl space where I see the leak. It appears that a small amount of water is traveling down the outside of the pipe and drips onto the crawl space floor. The toilet, garden tub, shower and sinks apparently all feed into the same pipe as they all appear to contribute to the leak. There is no apparent leak if I observe the ceiling from the first floor. Do you think the leak is most likely from a 90 degree fitting on the second floor or could it be somewhere in the vertical pipe traveling through the first floor wall? The pipe travels behind kitchen cabinets and countertop so it is not an ideal place to start cutting into the drywall. Any thoughts on how to approach all of this.