The pipe he used was 1 1/4" in diameter, but any left over piece would be fine. If you don't have a cap on hand (and who does) you'll have to hit your neighborhood hardward store, but the piece was pretty cheap.
He cut the pipe so that it was about 1 foot higher than the pot and glued the cap onto the pipe. He drilled random holes through the lower 2/3 of the pipe.
I used an old piece of rebar to loosen the soil
The rebar makes room for the pipe to go in
The pipe makes it easy to get water to the roots of the plant.
By adding liquid fertilizer, compost tea or worm tea to the pipe you can get nutrients to where they are most needed.
Be well and happy gardening!