Technical Sealant for boost gauge insert

[Sm1thygp]

Hi all, I've recently fitted my boost gauge and where I have drilled into the pipe I need to seal the nozzle I've used. I've used a inline nozzle where one side is bigger than the other so when I drilled it in I just made sure the hole was smaller than the nozzle. It will not come out but I just want to make sure there is no leak, can anyone recommend a sealant best for this? Cheers