Pick up the incorrect statement regarding a master trap from the following :

• It is provided in between the lower end of the house drain and the street sewer
• It is provided a cleaning eye at the top of the trap
• The height of fresh air inlet pipe fixed vertically with wall is 3 m
• The mica flap valve which opens inwards only, is fitted at the top of the inlet pipe
• The water seal is less than that of ordinary traps.