There is no hole in the top but the traditional plain ones I have from Morocco have a small hole in the side of the cone that you plug with foil or similar (a primitive blow out valve). The lids are very heavy, believe me, and are more than enough to keep the food under pressure. If you have a tagine that is highly decorated then it hasn't been made for the stove top, so don't use it. And of course your steam condensating method is also very true, but the whole process is speeded up because of the pressure, I'm led to believe.