Tubes left with samples in them for a period of time frequently present a challenging cleaning problem. Sample degradation or precipitation can cause material to adhere to the inner walls of the tube. Rinsing the tube doesn't always remove this adhered material. It's therefore often recommended using strong mineral acids such a concentrated or, in severe cases, fuming Nitric Acid soaks of 1-3 days, as needed. Nitric Acid can oxidize many organic chemicals and dissolves most inorganic materials, as well.  A final rinse with distilled water or Acetone is also appropriate.

Tubes which contained polymeric samples can be even more difficult to clean. When the polymers are natural products, like proteins and polysaccharides, strong acid soaks will usually be sufficient. However, when dealing with synthetic polymers, the challenge is more severe, since many polymers are inert to acids or insoluble in organic solvents by design.

Although polymers may not readily dissolve in solvents, it may be possible to soften them by soaking the tubes in a solvent that swells the polymer. Then a pipe cleaner might be sufficient to remove the softened material. It may take some experimentation to find the solvent combination that works best with your polymer system.