Modified single-stack sanitary system

• This system is used in buildings which have close grouping of the sanitary appliances. 
• Branch waste and soil pipes are installed wihout individual ventilating pipes. 
• Branch pipes which may serve ranges of up to eight WCs are normally 100mm bore. 
• Branch pipes for range of urinals are normally 50mm or 75mm bore. 
• A 38 mm bore branch pipe from a bowl urinal however, should be kept as short as possible. 
• For ranges of up to four wash basins , trap ventilating pipes are not required providing that the waste pipe is straight.