Once everything is good and dry, you're all set to go. I use a funnel to get enough water into the fill tube to let it wick into the sand. It takes a few minutes and the pot gets wet around the edges pretty quick.
Unfortunately, the last few weeks around here have had miserably high dewpoints. I did a test indoors where the air temperature was 77 degrees Fahrenheit but the dewpoint was over 60 degrees, so the inside of the can only got down to 75 degrees. I'll need to test it further when it's drier.
Fortunately, the whole point of the exercise was to make coolers for beverages while I'm in the August desert of Nevada for the Burning Man festival
. The air temperatures can get over 120 degrees Fahrenheit but the dewpoints stay very low -- around 35 degrees or so. This is the ideal environment for a terra cotta cooler so I'm looking forward to how well it works.