Suction cups will stick to clean surfaces that are both smooth and non-porous, like white acrylic shower lining, vitreous china, non-coated glass, mirror and smooth, shiny tiles. Wet the back with water before sticking. Suction cups won't stick to rough or porous surfaces, like textured tiles or paint because they can't form the vacuum needed to work.
You will get a pvc suction cup by default with each accessory product. If you're happy with this, stick with it.
If you want extra pvc suction cups they're here. Extra suction cups are useful if you have a shower dome so you can more easily relocate your bars into the fresh air from time to time. Nanotape won't work for this purpose but a spare suction cup will.
If you prefer a natural rubber suction cup as a substitute or in addition they're here for slimline ones - good for acrylic and glass and here for surfaces that are a little trickier. Rubber suction cups do not fit the Hookups.
If you have a textured surface or one that is unfriendly for suction cups you might like to try the nanotape backings (they come in twos). We can't guarantee it for all surfaces but it certainly works on more than the suction cups. Your can give nanotape a try as a substitute or in addition here.
Want to use your Block Dock on a flat surface? You'll need a Base. It fits all sizes except the Limited Edition Double Dock.