Can I Pour Boiling Water Into My Sink Drain? If your water pipes are made of Pex, CPVC or PVC - they are NOT made to withstand the temperature of hot, boiling water. If your water pipes are made out of Iron, Copper or Galvanized Steel - you certainly can run very hot water through them but if there are any rubber or plastic joints - those can get damaged over time as they are not made to withstand such high temperatures. If your sink is porcelain - Boiling/Hot water can cause minor cracks in anything made out of some form of china (sinks, toilets, tubs, etc.).