$(".connectedSortable").sortable({
  connectWith: ".connectedSortable",
  opacity: 0.7
});

$("ul.receiver").live("sortreceive sortremove", function(event, ui) {
  var id = $(this).attr("id") + "-empty";
  var listData = $(this).sortable("serialize");

  if ( listData === "" ) {
    listData = {}; listData[id] = "true";
  }

  $.ajax({
    type: "put",
    data: listData,
    url: $(this).attr("data-url")
  })
});