The use of drip or blow-off valves for draining fire services shall be allowed only in cases of absolute necessity, as determined by the Department, and in no case shall their installation be permitted unless furnished with a valve, which shall be approved and sealed by the Division of Water Distribution, and the end of every such pipe shall be exposed to view at all times. The size of drip or blow-off pipes shall be as approved by the Division of Water Distribution in each case.