I've been using vac hose with my KK in the last at least 5 yrs with no problem except air somehow gets in the system. I think that happened even when it was brand new and even when used with the KK original hose from the beginning. Actually, I changed out to vac hose thinking it's has less chance of getting air in since it's a one piece.
Again, I am trying to find out why the KK gets air in the system. I think it's the design (how the block switching position to move the KK) but I just wonder if anyone here uses KK with no air problem.