What is the impact of pouring bleach down the drain?

It is standard practice to dispose of used bleach solutions down the drain when connected to a municipal sanitary sewer system with copious amounts of water. Bleach is typically a 6% solution and after use it is typically less than 1%. Run a liter of fresh water for every 100mL of 1% bleach to reduce it further and everyone will be happy. The fate of the bleach in a system as large as most municipalities is just salts that have no adverse effects down stream.

If you are connected to septic system with a lateral field, then you may want to reconsider the disposal method. If it is a small amount, say 1 liter, then you may be able to get away with dilution down to .01% without ill effects as long as you don't do it too often, let's say once a week. Septic systems are not designed to have too much salt in them and this can be bad for the vegetation near the lateral field since it will build up over time.

Neutralizing bleach it typically not recommended since you can potentially generate toxic gasses if you aren't careful.

Bleach is a powerful, toxic substance that should used carefully and properly, and pouring it down a drain is not a proper use. Bleach can react with other substances in your pipes, potentially release fumes, and further plug up the system.. Although good at cleaning and disinfecting, bleach does not help keep drains clear or remove built - up gunk, since it has no effect on things like grease, food scraps or hair. Bleach can mix with compounds in surface water to create a number of hazardous toxins

I am in agreement with Ron's answer. Disposal of dilute solutions of bleach (6% sodium hypochlorite) down the drain is permissable under most standard chemical waste disposal guidelines. The key is dilution and knowledge of the reactive chemistry of chlorine - for example a really bad idea is to mix a strong base with the chlorine during disposal - exothermic reaction producing chlorine gas. Strong bases should be disposed of in segregated chemical waste. It is important to consult with the institutional chemical safety officer to be sure you are in compliance with local and institutional guidelines. Several important points. 1. Commercial bleach (used in home laundries) is added to sanitary sewage during normal laundry operations. 2. It is not corrosive enough to damage copper, iron or plastic pipes. 3. By the time it reaches the sewage treatment plant, it has been diluted sufficiently and reacted with organic not to harm the bacteria in the biofilter and sludge processing organisms in the plant. It all comes down to concentration, dilution and knowledge of simple chemistry.

Of poured down the drain undiluted, it will kill many microorganisms in the sink before it gets diluted and less effective. It *will* get diluted, and the bacteria will reproduce to satisfactory numbers to continue their degradation activities before removal during wastewater treatment. So there isnt likely to be any long term problems unless of course extremely large amounts are poured, which would be worrying.