Just because a sample gets sent to a lab doesnt mean that an adulterant check will be automatically performed.
Its to be remembered that the person who is paying for the UA (employer, PO, private person, etc) is the one who decides if a adulterant check should be performed on the sample. There are some budget-minded employers and POs who skip the adulterant checks and use the cheap drug screens to keep costs down. This explains why some people have used bleach and passed. When a drug check is the only check performed, anything from yellow colored hot water, dog piss, to bleach would pass those.

Always know what type tests you'll be taking before taking counter-measures. Check those test codes on the drug form.