Chlorine is a light yellow gas, second from the top in the halogen group (Group 17) on the periodic table. Although it is highly toxic (it was the first poison gas used in World War I), its extremely pungent smell is fair warning. Breathing in small amounts of chlorine is not bad, but larger amounts cause burning of the mucus membranes and lungs.
Bromine, on the other hand, is a reddish liquid that smells similarly, although some say that the smell is less repulsive. Bromine has the additional hazard of being spillable, and liquid bromine evaporates twice as fast as water AFAIK.
Both of these poisonous elements have one property that enables them to be easily, quickly, and completely neutralized. They are strong oxidizing agents. The chloride and bromide ions are harmless, ionic substances in most cases. Therefore, reduction can be used to remove chlorine gas.
For example, if you want to produce some pure manganese(II) solution by dissolving some pure manganese dioxide from a tantalum capacitor in hydrochloric acid, you will produce a large amount of chlorine gas. However, the reaction needs to be heated, so placing it outside on a normal day will slow the reaction very considerably. To prevent gassing yourself in chlorine or bromine gas, you may use a variety of reducing agents. Sodium or potassium metabisulfite, readily available from brewer's shops or chemical supply stores, is a good reducing agent. Mix this with sodium carbonate solution to form a basic reducing solution. Chlorine dissolves easily in a basic solution, forming hypochlorite and chloride. The hypochlorite is easily reduced by the sulfite ions. For a beaker, soak a rag in this solution and place it on top of the beaker. Use the bottom of another beaker if needed to hold the rag down, making sure that all of the chlorine contacts the rag. For a test tube or flask, use a scrap piece of hose (chlorine tends to damage hoses) and lead to a beaker with carbonate-sulfite solution. For a vial, wrap a tissue soaked in the solution around the cap to absorb any produced gases.