I started pumping after having made big length gains from manual stretching. I was hoping to make more length gains with pumping and have tried 5 different size tubes. From tubes that are 1” smaller than my erect girth ( obviously entered that one flaccid ) to full package pumping. In the end I gained zero length from pumping. I think a newbie can get results from pumping alone because they have some easy gains to be made. For me, pumping just can’t give a strong enough longitudinal pull for any meaningful stretch without going def-con 1 with the vacuum pressure. At my longest I gained almost 2” from manual stretching so that is my recommendation for length. Everyone is different though, so your results may vary. Take a few notes and abandon what doesn’t work after 3-6 months. I do think pumping has helped me gain girth on the bottom third of my shaft though, so it is still part of my routines.