Can you tell me what the square puddle in my drain is? Is it the inspection hole of a blocked pipe? I flushed the loo & ran the kitchen tap & that water ran through the 'y' shaped pipe on the left. When I ran the garden hose down the rainwater gully, I expected to see the square hole pipe flow but it didn't. What is that square puddle? & also where does my rainwater go? I could hear the rain water from my hose flowing but I couldn't see it. Does my rainwater exit through my neighbours property? Do I need to get that square bit emptied out so it flows? I ask because my water company previously said my sink drained incorrectly. We've rebuilt the kitchen since but I want to reassure myself it was all connected correctly. Many thanks.
Your rainwater may go into a soakaway, rather than into the sewer. That's worth checking out as you can get a reduction on your water bill if that happens - see here for more information on that.
My guess ( and it would be a guess) is that the square is linked to the soakaway - if water was meant to run through that part of the drain, the square would lead into a pipe to take the volume of water away but it doesn't - the water in the square section would only reach the Y pipe if the square filled up so much it overflowed.