Avoid throwing it to the sink because it can cause pollution to the environment. Better keep it in a waste jar and consult your university to know waste disposal regulation. I believe the disposal regulation is different per locality/state

We keep it in empty media bottles, they will be disposed properly later by the staff

Thank you for your suggestions.

I feel that California has stricter rules than Texas. I will try to collect the solution in a bottle and let the staff dispose of it later.