Like a lot of real poisons, we're talking minutes and - in d20, where characters are routinely superhumanly durable - relatively minor effects. Bleach is pretty obvious in most foods or drinks and applying it externally won't really bother you much (I've spilled plenty of bleach on my skin doing laundry). Applied to a blade, it will tend to be washed out by blood, and will simply result in a nice sterile wound and some local irritation: you're very unlikely to get a serious dose into someone that way. A direct injection would be pretty bad, but so is a direct injection of almost anything but water or blood.
Overall, drinking diluted bleach normally causes stomach irritation. Stronger doses tend to cause physical damage to internal tissues, difficult to treat in the real world, but just HP damage in d20. A cure light wounds and a neutralizing agent should fix a victim right up. An injection is reasonably toxic, but so is a straight injection of alcohol (of any variety), clay in water (will cause clotting and other problems), air (not exactly toxic, but likely to cause lethal embolisms), and hundreds of other substances. Most effective d20 poisons are blatantly supernatural.
