This is a problem that’s been long discussed I am sure.
- One of the biggest things to consider are the pump itself. I know that some of the cheaper ‘one-size-fits-all’ pumps are more prone to this issue. The problem is the much larger tube circumference to the penis itself means the negative pressure will start to pull on any loose skin to pack the tube as that’s a much weaker point to equalize than filling and stretching the penis itself.
- Lube on the scrotum itself. (another issue with cheap pumps that use the silicon rings to make the entrance smaller; they generally get lubed and do not offer much resistance to avoid pulling your sack in)
I only just purchased a nice cylinder that fits correctly, which should arrive tomorrow so I can give some more feedback on how that helps from personal experience later. For the time being, I suggest;
1. Careful with the lube and be diligent of what gets lubed, maybe keep a towel near to dry some areas.
2. Pull your sack down when increasing pressure, if it starts to slip you can generally pull it out although a pain
3. angle the tube differently, I would usually get all the way into the tube and push it toward my pelvis while pulling my scrotum away before starting to add pressure so the available skin was decreased; and then again continue to pull as I increased pressure to avoid it slipping inside.