Hi do you mean rainwater and storm water drainage rather than a sewer? I dont think toilet sewers ever ran under a house but the pipes that drain front of gardens can- the one serving our house runs under our neighbours house and connects to the main sewer running along all of our back gardens. Ours are 1930s houses but the mains sewer at the back started off with the Victorian houses further up and the developer of our row of houses connected into that existing sewer. its pretty normal I think but you might want your surveyor to have a look at the condition of the pipe.