1. Pull the gripper hole over the knob end of the P-tainer, dots facing out.
2. Flip the gripper up out of the way.
3. Set the dome end of the P-tainer over your glans.
4. Hold the P-tainer against your glans by the knob end with your non-dominant hand.
5. With your dominant hand, wrap your thumb and index finger around the bottom of your shaft and pull up on the skin while pushing the P-tainer into your body, rolling whatever slack skin you have up onto the body of the P-tainer.
6. Use your other fingers on the hand holding the knob to flip the gripper down over your skin.
7. Pinch the outside of the silicone to smooth out any wrinkles. The skin should sit flat, with the tip near the circle at the top of the gripper.

Full walkthrough with pictures and video: How to Wear Your P-tainer.

Give each one a real wear — long enough to sit, walk around and forget about it. You're looking for the one that holds without pinching and stays put without you thinking about it.

• Too much tension, or it pinches? Try one step shorter.
• Slack skin, or it works loose? Try one step longer.
• Feels tight around the body, or leaves a mark? Try the next diameter down.
• Skin won't stay rolled up? Try the next diameter up.

The demo kit steps in 10mm increments. If the standard and the +10 both feel slightly off in opposite directions, the +5 between them is probably your size — our full range steps in 5mm.

The string has a pre-tied loop at each end. Loop one end around the knob end of the P-tainer and the other around the neck of the water bottle.

Fill the bottle part way and add water until the tension feels pleasant — around 8oz, roughly half a bottle, is a reasonable place to start. One ounce of water is almost exactly one ounce of weight, so the bottle doubles as a rough scale. A full 16oz bottle is right about a pound.

When you want the exact number, hang the bottle from the tension gauge. It reads to 500g / 20oz.

Tie your own loops: the string comes with loops already tied, but knots in this cord work loose over time. Tie each end yourself with an adjustable grip hitch, at the length that suits you. It grips under tension, slides when you want to change the length, and won't shake itself undone.

If you want to feel something genuinely interesting, swing your hips a bit with the weight attached.

Nothing should ever hurt, go numb, or change colour. If it does, take it off and give yourself a break. If something doesn't feel right or you can't get it to work, get in touch — we'd rather hear from you early.