$re = '@<tag-1>.*?</tag-1>@s';
$str = '<p>You will find below reports for customer <b>[CustomerName]</b> dated <b>[ReportdDate]</b></p>
<tag-1>
<h3>Title1</h3>
<table>
<thead id="t01">
<tr>
<th align=\'center\' width=\'80\'>Order Nr</th>
<th align=\'left\' width=\'400\'>Planning date</th>
<th align=\'left\' width=\'200\'>Info</th>
<th align=\'center\' width=\'200\'>Site Name</th>
</tr>
</thead>
<tbody>
[TableTodo]
</tbody>
</table>
</tag-1>
<tag-2>
<h3>Title2</h3>
<table>
<thead id="t01">
<tr>
<th align=\'center\' width=\'80\'>Order Nr</th>
<th align=\'left\' width=\'100\'>Date</th>
<th align=\'left\' width=\'400\'>Info</th>
<th align=\'center\' width=\'200\'>Site Name</th>
</tr>
</thead>
<tbody>
[TableTodo]
</tbody>
</table>
</tag-2>';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php