One tricky part was how to attach the large back hose to the helmet. I wanted to be able to unattach the hose at will, and also to have it pull away if snagged or pulled rather than ripping the helmet apart.
For the main hose I used a washing machine drain hose. I’m guessing it’s about 1 1/2 inches in diameter. The hose is hard plastic but the top part is rubber, which was good luck for me. I cut down the rubber top but left a ridge that I could compress and slide into a smaller hole, then it expands again and holds the hose in place. I was also able to drill a hole into the rubber to attach the smaller hose.
All the details in place, this helmet is ready for Plasti Dip.