Some experience with “suction” achieved by Onaholes:
- The toy must come with a round entry that seals well.
- The toy must have a relatively large chamber at the end.
- The toy must not be open-ended.
Before entry, squeeze the end of the toy to expel the air inside. This creates a vacuum that causes the toy to suck onto your member more tightly.
For active suction one may find interest in motorized toy such as the Suck-O-Matic, Venus 2000, or a low-budget DIY milker.