This is a minimal filler tube - its made from 40mm PVC waste water tubing about 75mm long. A shallow grove is cut all the way round.

Shot showing internal spacer - about 15mm thick super-glued to both the outer and inner tubes.

Balloon Neck pushed over the filler tube - Totex balloons are a tight fit.

And secured with a cable tie that sits over the grove.

For Hwoyee balloons fold the neck over and tie.

The grove and the cable tie ensure the neck is well secured.