Tinymce content clear mceCleanup
TinyMCE provides a method setContent. Use this method to set new value.
tinymce.activeEditor.setContent("content");
Similarly it provides getContent()
tinymce.activeEditor.getContent();
Use :
tinyMCE.activeEditor.setContent('');
Sets the specified content to the editor instance, this will cleanup the content before it gets set using the different cleanup rules options.
Reference:TinyMce
Hope it helps.