If you have never used PWT before, it is recommended to use it for the first time while the house is empty. Because PWT cleans the water lines so thoroughly, dislodging lots of biofilm and residual material in the lines, a high pressure flush is needed to remove that debris from the water lines. Using PWT with birds in the house for the first time will make it difficult to remove all of the debris dislodged by the cleaning process possibly causing clogged nipples and birds to ingest the dirty material.