Draining containers without holes

My gardening books all warn against potting plants in containers without drainage holes, so I’ve found a way to use the pottery crocks I buy at country auctions as planters by installing a drainage pipe at the time I fill each pot with soil. I cut a 1-inch-diameter PVC pipe as long as the crock is tall and cover the bottom end with a bit of nylon net screening. I position the pipe upright on one side of the pot before filling the pot with soil and plants. After a heavy rain—or if I suspect that I’ve used the watering can too generously—I tip the pot sideways to allow excess water to drain away through the pipe.