You might be wondering what one earth's a piping bag with coupler ring? Well, it is generally used for icing cakes and looks something like below and consists of two parts: the base and the ring.
This is my version looks something like it's just been squashed by a truck:
First, you take your old chamber and place it on top of the bottle cap. Then, draw a circle on it. Using pen knife, make a nice round hole through the cap. You'll get something like this:
Homemade icing coupler (with the tip enter-frame :P )
The assembled parts