I have a irrigation tap,(if you will) on my pond before the drain valve on a four in pipe and with around 28 to 30ft of head pressure I can get a lot of volume that I fill watering tanks with and also spray rigs, granted the pressure is not great but I have a 1 1/2" line to fill with, takes no time to fill a tank, also at that depth the water almost smells septic which seems to make the plants grow.
And as for tapping into a 12" pvc, its a piece of cake, the water companies do live taps everyday with a tapping tool that you can usually rent from your local water and sewer service pipe supply place, or just buy the band from them for whatever size syphon pipe you have and whatever size tap you want for your irrigation pipe and install it on your pipe when it is empty sometime. Good Luck!
