Step 1: Get the stuff
1 - a bucket (or small waste bin) 5$
2 - 1/4 inch tubing. I got some drip irrigation tubing. It was the smallest & cheapest there. 13$ for more than I'll ever need
3 - as many of these as you need holes. They are rubber doughnuts with a grove on the outside. Get it the same diameter as your tubing. It will fit snugly and there won't be any leaks. Or messy silicone or epoxy to seal it. 4$
I was doing this last minute, so I went to Home Depot and probably spent more than I should have. But I want my balcony tomatoes to survive my 10 days away from home. And in this heat, they need to be watered almost every day...