Constructor and Desctructors in PHP? Do I need to delete/clean stuff? [PHP5]

[Shaitan00]

I've created some PHP classes that, in the constructor, create an instance (object) of another PHP class (for example a database), does this need to be cleaned up somehow? For example is there such a thing as a destructor [function() ~function()] in PHP5 and is it needed?

For example - check out the following code I have for a class called Tools.class.php (for example)

{
    private $db = NULL;             // Database Interface

    ////////////////////////////////////////////////////////////////////////////
    // Constructor
    function Tools()
    {
        $this->db = new Database();
    }

    function DoStuff()
    {
    ... do stuff ...
    }

So, in the constructor of tools I create an instance of Datbase ($db), and then in DoStuff() I use that connection to get/set data from the Database ... All this is great but what happens when Tools is no longer of any use? Meaning I have a PHP file that does:

$tool = new tools();
$tool->DoStuff();

But that is it ... Do I need to delete $tool somehow?
And within Tools.class.php do I need to somehow cleanup $db?

I don't want to cause any memory leak or Database connection issues.

Any help would be much apprecited.
Thanks,