TM M870 hpa help

[cropzy]

Hi lovely forum people.

I have a strange issue adapting a TM M870. It has already been hpa'd but I am changnign the grip/stock on it and need some help.

Here is the setup I am having. A 3d printed grip adapter and grip. Don't worry, they fit and are printed at 100% infill and hold the weight perfectly.

The issue is with the adapter: https://pinshape.com/items/32629-3d-printed-hpa-grip-for-tm-870
Here are the instructions:
This adaptor will make your gas tm870 to hpa  you will need to make threds  2x m5 (one for the m4 gbb grip one for the tube in the backplate) 4x m3 (in the back plate) you simply take off the hose on the cylender and replace it with a new flexible one. (6mm) heat op the end that are going on the cylender and press it on. then put your hpa grip on screw it to the m870 after that. drill a hole to your m4 gbb grip.mount the m4 grip  put down the hose. put on the back palte with 4x m3 hexscrews

The thing is, this grip says you have to attach a tube directly to the valve, which doesn't have a notch. See photos below:


As you can see, this just slides on and secures with a bolt. The actual metal part on the shotgun is where a 6mm nylon HPA hose is supposed to go on. I am supposed to heat one up and then just slide it on. I am worried that the pressure will blow it off as there are no notches.

Here is the original tap and setup when it used a long stock:


As you can see in the last picture, it has an oring in it as well.

So I ask you people, what is the best way in doing this? Would I just be able to put a 6mm hose on the cylinder if I heat it up and will it stay there. Or am I looking at a different approach. I want to keep it short as the first picture. If need be I can sand things down.