I also tried this and found the draining method to be quicker and more effective. you just need too much stone that can be otherwise used for building purposes

just place a portal down and travel the stone to your building place? no need to waste them resources

Even if this works, it's a pain in the *** to do. There is around 90-115 pieces of tar in every pit and you will not get all of them with that method.
Just drain the pits from tar by pick-axe a deep trench towards the pit. Start a distance away and work your way into the center. Those pits that are very close to a ravine is the easiest one to drain.

wow, really? I'm about to head to my first tar pit, gonna check this out.