[flybouy]

You need to purge the air from the entire system including the outside shower. Water will not compress, air will. Air trapped in the water lines will compress and over time the water can incorporate into the water causing the pressure to drop and the pump to energize briefly. Purge the entire system then if the condition persists you either have an external water leak or an internal one (pump diaphragm not holding or check valve not holding leaking water back into the tank).