These are very high quality HDPE Barrels that I have setup for drip irrigation. 15 gallons each. They are drilled and fitted with 1/4" drip irrigation tubing.
They work very well to fill quickly and then they slowly water the tree and let the water go down deep to the roots for optimal watering.
They sell products for the same purpose commercially but my barrels are far more durable and will last for many years. For example: