I have a stubborn clog in a garden style tub. All the chemicals have not worked. I am trying to snake the drain but can not get the cover off!! This is a newer home, 5 yrs old. The cover is one you twist one half turn while pulling up and the drain is open. Problem is that the opening is not big enough to get a snake through. I have tried unscrewing the top but it comes off leaving the drain covered. HOw do I get this cover off!!!