I too use Cask Widge, but that is by-the-way. You can get 8mm push-fit to 5 or 6mm stem reducing adapters quite cheaply (not JG; if they were they wouldn't be "cheap"!). The silicone tube (5 or 6mm ID, 10mm OD platinum cured "milk pipe") is pushed on these and crimp held (if necessary).
View attachment 78987
The pushfit end fits to the short 8mm dip-tube (not too short or they won't come off easily!). I run a tube cutter carefully around the dip-tube to score it (pictured) and give the pushfit something to grip to. If you haven't got a long "short" (gas-in) dip-tube, cut one from the now obsolete long (beer-out) dip-tube (about 40-50mm).
I've just received the "Corny keg" post bulkhead assemblies (homebrew sites and Amazon) having been inspired by
@Davegase's post. I'll fit it to a spare "Corny keg" lid, Unlike
@Davegase I replace the original long dip-tube but I've got a blockage in a dip-tube in a keg full of beer! This assembly should rescue the situation without dipping my hand in the keg's beer!
Having the dip-tube removeable is a great help when cleaning the dip tube because they are inclined to accumulate difficult to shift yeasty deposits (you won't know if this happens using a rigid SS dip-tube!). I've a pipe cleaner (pictured) to keep them clear.
The "milk hose" (tube, pipe, whatever) should be just long enough for the extractor end to reach the bottom of the keg. No longer!