None of the commercial test kits will tell you if you have pipes in your pill. Off the top of my head there is one Piperazine that will react slightly to one of the reagents, if I am correct it is MCPP that will turn Simons blue, however so will MDMA and Methamphetamine. Generally if you do not get a reaction to the test kits you should not be consuming the pill. Even if you do get a positive reaction a pill could still possibly contain piperazines as the test kits only tell you if the pill contains the substance you are testing for.
Users have reported fizzing when testing for piperazine as seen in
this report. I suspect it has to do with how much piperazines they shove in the pill, similar to how good molly will fizz. Perhaps P_D could explain this?
Pills with piperazines in generally like to retain moisture from the air, this is why most pipes seem to yellow or darken over time or look like they have yellow spots on them. Here is an image from one of ekstasis' reports.
Slight yellowing on pipes.
However here are pipes with no yellowing like the above.
Images are
from this thread here.
There was a thread with great pictures of pipes that were left for a few months and how they change in colour, I can't seem to find it. Perhaps someone else knows which thread I am talking about.
Users will report pipes having a sour taste, I have licked one piperazine pill in my lifetime and can confirm the sour taste. This however is not a good way to test you pills. Whatever is used as a binder could easily block the taste.
If you have any more questions feel free to ask.