Adsorption of methylene blue and malachite green was carried out using "Luffa cylindrica" sponges as adsorbing material. We provide a very illustrative exercise about the use of common natural materials requiring little preparation to solve environmental tasks in a routine laboratory situation such as using dyes. In addition, the experiment can be used in different study levels. We illustrate the use of spectrophotometric techniques, calibrations, or (in a more advanced level) calculations of adsorption kinetics and the use of statistical tools in data treatment. The use of natural fibers to remove dyes from laboratory wastewater highlights the environmental responsibility of undergraduate students by training them to treat common laboratory pollutants, and on the other hand, it offers an efficient tool to illustrate water remediation procedures.