Help me figure out the drains at my house (Pics)

I_have_spoken

As title, bought a house where the attached garage was extended to the rear and a tiny toilet cubicle installed. The framing and WC has since been removed, leaving some puzzling things...:huh:

The soil stack seems to be open-vented at the top, with a 'cone' device with slots all around.

The WC and wash-basin used to connect the multi-boss unit at the base of soil stack.

I'm puzzled by the three access points in the poured concrete slab, not sure if these pre-date installing the toilet at back of garage or were to do with the installation.

There's two man-hole covers in the front drive which line up pretty well 100% to these three access point on the back patio.

The bathroom in the house is on 1st floor in the back corner, garage side.

Ideas?

keystone

So what can you see when you open them up?

Cheers

anotherbaldrick

Look like rodding eye gullies to drain surface water from the paving. But why 3 ? perhaps the external works subbie found he had 3 on site so decided he might as well use them

I_have_spoken

So what can you see when you open them up?

Just the top rim of clay pipes which then curve at 90deg leading towards the back of the garage

Look like rodding eye gullies to drain surface water from the paving

Unfortunately the concrete flag outside the door has 'sunk' and the water actually disappears down that gap between the slab and the concreting along the step :eek: