Dear  Louise, It has been my experience to change the tubes to help wean.  If
the baby is on the large tube go to the medium ...however you still must
observe the rythmn of the suck swallow... if not.. the baby is not ready to
transition.  The same if the baby is on the medium tube go to the small tube.
I also don't open the flow until the baby finishes with the let down or if
the baby will not suck.. open the tube until the let down occurs and then
turn it off until the let down is over. The main thing to remember about the
SNS is when the baby does not need the formula in the SNS the formular will
not drain or will drain so minimally 1/4 to 1/2 on ounce. The SNS must be
attached correctly for this to work.  By comparing the weight of the baby to
how much formula taken we can tell that the baby really does not need the
formula or needs the formula.
Hope this helps  Camille