Air in water pipes Home › Forums › Archives › Old Bulletin Board Archives › Air in water pipes This topic has 0 replies, 1 voice, and was last updated 22 years ago by wcplumb. Viewing 0 reply threads Author Posts 28 Feb 1999 at 11:02 am #280580 wcplumb 2 story home. 1 toilet causes pipes to knock when flushed. Ive turned off water, flushed & open all faucets to drain system. Problem diminished but still present. Any suggestions? Author Posts Viewing 0 reply threads The forum ‘Old Bulletin Board Archives’ is closed to new topics and replies.