commentform: Issue: "http://website"

Hello!
I’ve tried various things, but I just can’t get it to work.
In the comment form only (user)name and e-mail are required by default, right? Website is not.
The way I set it up, it always displays “http://website” if somebody doesn’t click onto the webiste input field to clear it.

Here’s my code in the comment.php:

<p><input type="text" name="author" id="author"  value="Name" onfocus="this.value=''; this.onfocus=null;"size="22" tabindex="1" <?php if ($req) echo "aria-required='true'"; ?> /> <font color="red">*</font></p>

<p><input type="text" name="email" id="email" value="Mail (will not be published)" onfocus="this.value=''; this.onfocus=null;" size="22" tabindex="2" <?php if ($req) echo "aria-required='true'"; ?> /> <font color="red">*</font></p> 

<p><input type="text" name="url" id="url" value="Website" onfocus="this.value=''; this.onfocus=null;" size="22" tabindex="3" <?php if ($req) echo "aria-required='false'"; ?> />
</p>

And that’s what I already tried, but it didn’t work:

add_filter('pre_comment_author_url', 'filter_comment_url');
function filter_comment_url($url){
    if ($url == "Website" || $url == "http://Website"){
        $url = '';
    }
    return $url;
}

Any other suggestions?
Thanks a lot in advance.