If you try to stick a household-grade suction cup to a textured surface, it will either not stick at all or it will fall away within a matter of seconds. Suction cups need to form a perfect seal against a surface in order to adhere to it, and any dips or bumps will allow air to flow beneath the rim of the cup. This prevents a seal from forming and makes the suction cup completely ineffective. Fortunately, suction cups can still be used on textured surfaces if careful steps are taken to prepare the surface beforehand.
Rub the area to which you wish the apply the suction cup using a piece of fine-grade sandpaper and minimal pressure. Continue until the surface is smooth to the touch. Sanding the area before applying the cup is essential; any juts or depressions will destroy the vacuum condition that is necessary to keep the cup attached.
Wash the newly-smoothed area with soapy water and a soft sponge. Scrub the surface thoroughly to remove any dirt that may prevent the suction cup from adhering.
Wipe the surface dry with a cloth instead of paper towels; paper fragments could cling to the surface and make it even more difficult for the suction cup to stick.
Spread a thin layer of petroleum jelly across the surface with your finger. The jelly will help to fill any remaining depressions and allow a tight seal to be formed against the edge of the cup. Skim off the excess jelly by sliding the edge of a credit card over the surface.
Rub a tiny bit of petroleum jelly along the inner rim of the suction cup, ensuring that the jelly is evenly distributed.
Press the suction cup slowly but firmly against the surface. If the cup sticks, leave it for 30 minutes and return to check that it is still solidly attached. If air has leaked into the cup and it has lost suction, repeat the steps until it remains attached for 30 minutes with no sign of loosening.