Why we want to see the bottom of the discharge tube

Pressure discharge tubes are found on water heaters and hydronic heating systems requiring a boiler and are needed to help regulate the pressure buildup due to hot water expanding in the system.  A little water should discharge from the relief valve through the tube onto the floor  when the system is heating up the and creating pressure.  If a lot of water is discharging after heating up this means there is a problem with the relief valve or perhaps an expansion tank.    Liquid should not discharge when the system is cold. This would mean there is a problem with the relief valve or expansion tank.  We can only see if excessive water is discharging from the discharge tube if the bottom of the tube is visible.  During approximately 30% of my inspections I find the bottom of the tube hidden in the crawl space or in a wall cavity.   If you can't see the discharge you can't see if there is any discharge. If the bottom of the the tube is hidden the fix it easy.... simply cut off the tube about 6" above the floor where the appliance is located.