safety - Neutralizing TCA washes

A neutralization reaction occurs between Brönsted acids and bases to form a salt.

In this case, you have to add a Brönsted base to neutralize your acid. If the final pH is important, you should work out the exact quantity of base to add. Otherwise, just use litmus paper to check the pH of your solution, and add base until it's neutral.

EDIT

In view of the other answer proposed, I want to stress the following:

Do NOT dispose of your solution in the sink/sewer. Leave it in its plastic bin until a lab technician takes it to the furnace.

If the base you use is sodium bicarbonate (NaHCO₃), there will be bubbling, caused by the decomposition of carbonic acid (H₂CO₃) into water (H₂O) and carbon dioxide (CO₂). You've successfully neutralized the TCA once there's no bubbling upon addition of NaHCO₃.

It is indeed best to proceed slowly while adding your base.