Laying soil pipe under floor

[Riki1980]

Hi
I'm hoping someone could advise me on what to consider in my case as I'm clueless about such things.
We are looking to get a downstairs toilet. The drain is at the back of the house and the stack pipe is internal and is in the middle of the house.
We had a professional come out and they said the best option is to connect a soil pipe to the stack. They will need to dig into the dining room floor 1.2 metres deepest drop to the stack. There are no walls between and it's about 4 metres distance.

I've checked and they are registered with checkatrade and trading standards. They also have liability and insurance.

I'm nervous about the thought of this as they are digging inside my property. Is there anything else I need to consider in terms of risk assessing? I believe there is no pipework underneath

 

[Mottie]

Our soil pipe goes straight into the ground as do all the houses in my street and the main drain runs along the backs of the houses. Only every third pair of semi's have an inspection cover in their drive and it’s not us. So, when we wanted a toilet just off the hall, it would have meant digging up the whole length of our drive, digging a pit and breaking into the main drain. Instead, I opted for a macerator where only a 22mm pipe was needed to remove the waste - straight into the soil stack at the rear. Works fine for us and has been in over 20 years. The macerator did pack up once so instead of fixing it, I just replaced it and at around £300 it was still less aggro and the expense of the drain work. The new one did pack up again when I chucked something down there that I shouldn’t but with advice on this forum, I fixed it for a fiver! They’re not for everyone though.