STP packer position
First of all, you need to make sure you position is correctly, you need to try to find the proper position and it takes some time.
Do not bent shaft too much
For each person, it is a bit different. Secondly, while peeing, you would need to make sure you angle and position the shaft properly without pressing it too much. In some cases, clients press them too hard this way pressing the funnel and blocking the flow.
Keep the shaft tight
Hold the shaft tight, while pressing two fingers, placed in the scrotum area, against the body.
When peeing you need to control the flow, meaning that you would need to stop the flow from time to time to make sure there is no overflow.