Then just dissolve it in water and pour it down the drain.
Follow these rules. Especially rules C and E.
If the material is in an aqueous form, it can be poured down the drain with excess water if:
a. Local and State regulations have been checked and you have verified that this material is suitable for this type of disposal
b. The school drain is connected to the sanitary sewer system.
c. The quantity that you are disposing of is minimal. A good rule of thumb is less than 250 mL.
d. Combinations of chemicals are not going down the drain at the same time.
e. A twenty-fold excess of water is used when washing the chemical down the drain.