Clear dependent drop down once other value is selected - php

Question

I have multiple dependent drop down which get from my database.
The first drop down will select eOpp and the second drop down will be based on selected eOpp from first drop down.
//First Drop down
<label>Select eOpp</label>
<?php erfq_generateOppDropdown($oppID,"erfq_rfq_oppID");?>
//Second Drop down
<label>Select Item</label>
<select id="item" name="item[]" multiple="multiple">
</select>
Here is my ajax to get value from first drop down.
function getItem(val) {
$.ajax({
type: "POST",
url: "get_item.php",
data:'erfq_rfq_oppID='+val,
success: function(data){
$("#item").empty().html(data);
$("#item").multipleSelect("refresh");
}
});
}
It works fine to generate both drop down. But when the first drop down (Select eOpp) has changed, the second drop down still will remain the previous value in my drop down. I use this multiSelect for my second drop down under the basics1. jquery.multiple.select.js
For example when I selected the first eOpp, the result will be like this:
Select eOpp: 1
Select Item:
Item 1(A)
Item 1(B)
But after I changed the Select eOpp, it will become like this:
Select eOpp: 2
Select Item:
Item 1(A)
Item 1(B)
Item 2(A)
It will retain the previous value where eOpp=1 but when I use php to $_POST it, I get no value. I have to remove the previous record accordingly when I change my Select eOpp
EDIT
The problem occurs when the multiSelect is implemented.
$(function() {
$('#item').change(function() {
console.log($(this).val());
}).multipleSelect({
width: '100%'
});
});

Answer 1

Destroying and reinitalizing should work:
$("#item").multiselect('destroy');
$("#item").multiselect();

Answer 2

After I have changed the multiSelect plugin, it works well with my code.
For more information, please see JSFiddle. A few changes of the function are
1) function MultipleSelect($el, options)
2) MultipleSelect.prototype = {
constructor : MultipleSelect,
init: function() {
var that = this,
html = [];
if (this.options.filter) {
html.push(
'<div class="item-search">',
'<input type="text" autocomplete="off" autocorrect="off" autocapitilize="off" spellcheck="false">',
'</div>'
);
}
3) optionToHtml: function (i, elm, group, groupDisabled) {