[DSW]

In a pinch where I couldn't damage the existing crete by drilling outside the old post, I've taken a sawzall and cut the tube wall from the inside. The trick is to cut as deep as possible, but not crash the blade in the bottom of the hole. I'll usually take the saw and try to extend the blade as far as possible before starting, then insert it in the hole and see how much clearance I have to work with. Often I'll use a "shim" of plywood or 2x material between the crete and the foot of the saw to try and cut down how far I have to hold the saw.

Note: you'll waste the blade as soon as it goes thru and hits the crete, not to mention if you crash the blade, so bring plenty of spares.

Once thru, you can usually take a chisel and fold the old tube inside to remove. If I've got a bunch to do, I'll use the chipping gun with the chisel. I've also split the tube with the chisel if I can drill a relief hole just outside the old pipe like you are thinking about doing.


My 1st choice is still core drilling as others have suggested. I'd simply rent one myself. They aren't that expensive usually. Go ahead and buy the bit if you can afford it. Most places make their money on wear on the bits they rent. Often you can buy 3 or more bits, for what they charge in "rental" for the wear.

 

[DSW]

If you did that most places I've worked, you'd be replacing the whole walk because of oil stains. "Used" oil usually is almost impossible to remove from bare concrete. Having an oil stain at the base of every post would pretty much pi$$ off almost all the customers I've worked for.