I have a 3 CFM pump and a 50mm tube this will pretty much do anything and will cope with leaky grips. I did try various pumps before opting for the current one and anything that was either hand or battery driven didn't seem able to cope. Have done around a hundred grips with my setup and it has coped with every type of grip. Let me know if you want more info.
I actually have mine working It seems the end of the tube isn't creating a seal(maybe GM we're onto something with the ridges).I used electrical tape to get a seal and the vacuum is pulled perfectly. Vid coming up.
Then a new question arises. How to make a seal that works every time? Without tape that is.
Make a slight groove in the tube to allow an o ring to sit in?