is it true that; if u drop a piece of comet or draino into a urine sample ...?

Question

...that it will make a positve result undeterminable? or aspirine?

Answer 1

If you're worried about passing a drug test... droping anything into the sample will get you a positive result. Labs that process drug tests are well aware of ALL the 'tricks' used to avoid detection. If they find the results undeterminable because of tampering YOU FAIL!

Answer 2

Drano: when added to urine, will often produce false negative results. However one of the drawbacks is that it can color the urine sample blue and put the pH outside the normal body range.