It can have several reasons: The sponges not having enough friction to keep in place in the can (place double folded sanding paper between the sponges and can), the sponges are to THICK (so it can’t ‘make room’ for the penis’), the sponges can be to THIN (it doesn’t ‘clamp in place’) what you can for example also do is put another set of sponges or an old T-shirt at the bottom to prevent the sponges from shifting -xXx-
It can have several reasons: The sponges not having enough friction to keep in place in the can (place double folded sanding paper between the sponges and can), the sponges are to THICK (so it can’t ‘make room’ for the penis’), the sponges can be to THIN (it doesn’t ‘clamp in place’) what you can for example also do is put another set of sponges or an old T-shirt at the bottom to prevent the sponges from shifting -xXx-