I filled an empty gallon water jug with water and put the lid on. Then poked about 5-6 slits in the sloping top of the jug around the lid (with a sharp knife ~ wiggle it a little when it's in there, so the slits are slightly open). Turn the jug upside-down (lid down) in your pot (mine was propped against a little solar light, to keep it straight).
The water should gradually seep out of the slits while you're gone. The jug collapses into itself as the water depletes.