My daughter has a feeding tube and we needed a portable solution to keep the pump and bag together while we're out.  I used a ¼" hex screw to secure the pump, but you should make sure that the screw has the same thread pitch as the pump before assembling. 

The bag fits securely in a groove and there's a notch for the tube end when not hooked up.

I printed this out of Jessie Ice Purple PLA without any supports.