If one has a reason to suspect that there is waste in their vicinity, they must check to make sure that there isn’t any around before reciting a Davar Shebikedushah. If one does not check, and then finds out after that there is, their Brachah or Tefilah is considered an abomination, and it must be repeated. However, if one does not have a reason to suspect that there is waste in their vicinity and makes a Brachah or says a Tefilah, and finds out after that there is, they do not need to repeat what they said.