Instead of the condesending reply why not use your obviously greater intellect to explain your comment? After all, this forum is all about passing on knowledge to the unknowing and in my case, not so bright, help me out
If you drill into steel you will generate heat, sometimes sparks. Drilling into a steel container still containing gas creates the possibility of igniting the gas when it comes out of the hole you are drilling.
Take valve out. Fill with water. Empty water. No gas. Cylinder is now safe.
I see no reason to doubt that the valve is screwed into the cylinder on a right-hand thread, irrespective of whether the cylinder held butane or propane and is therefore unscrewed by turning it anti-clockwise.
The thread on the valve that the appliance or regulator screws into is left-handed for propane and right-handed for butane to prevent the wrong gas being used for a particular appliance.