I am trying to make a millstone fountain. I have the millstone that has a 3 inch square hole in the middle. What I cannot figure out is do you have to plug that hole and put a tube through it? Otherwise the bubbling of the pump just fall back into the hole and won't go over the whole stone. Does anyone know how to do this? I've looked all over and can't figure out how this should be done. Thanks for your help!