The best approach is to remove the slip first and work on the adhesive afterward.
Remove the strips by slowly raising the edges of the strip using a knife. Once you have raised enough slip to hold with your finger all you have to do is pull.
Using a clean cloth soak the remaining adhesive with a solvent for 20 minutes. You can easily get a solvent removal adhesive from a local store. However, alcohol, baking soda, kerosene, furniture polish or vinegar can do the job just as well.
Wiping the surface will get rid of most of the adhesive.
In case there is some left on the bathtub, you can take a scrub and work on the surface until you end up with a clean surface.
Another option is to use heat as opposed to solvents.
Cover the bathtub surfaces strewn with residue with tinfoil from your kitchen.
Heat the foil with your hair dryer to soften the non-slip stripsUsing a sharp knife, lift the strips and pull.
The next option is to soften the surface using hot water or vinegar.
Using a thin hard object such an old credit card, scrub the surface as hard as you can until you have cleared all the strips and adhesive residue.
Rinse and wipe with hot water to get a clean surface.
Finally, try this option of investing in a strong adhesive removal solvent. Most people recommend WD – 40. Pour the solvent on the decals and let it stand for about 20 minutes. The solvent will make the decals soft so they will easily peel off.
For a cleaner surface, you will need to wash WD-40 using soap and water.