After sinking 50cm into my back yard a few weekends ago and loosing my flip-flop I figured that I would have a look at some old photos to see where the plumbing was run under our back yard.
If you have a look at the photo on the left I actually sunk into the mud pretty much directly over the top of the new kitchen plumbing drainage pipe that was run through the back yard.
When they ran the new plumbing drainage after lifting our house they put some of it into the concrete slab, but a large amount of the plumbing drainage was run under the ground beside and behind our house.
Because the climate here never gets cold a lot of the plumbing is run down the outside of the house. It is very different from what I grew up with in Canada, where everything had to be way under ground, or inside the insulated walls, otherwise they would freeze and explode.
When they filled in the massive hole that they made for the plumbing in the back yard I don’t think that they compressed the soil at all. It was probably assumed that over time it would compress itself, but with the extremely heavy rains that we’ve been getting the soil over the plumbing just became so waterlogged that it turned into a sort of “quick sand”.
One thing that was interesting that we found out while planning the plumbing and drainage is that our neighbours sewer line actually runs through our yard for their second bathroom. This prevented us from having a larger deck, not that it matters any more though since we are no longer doing a deck.