I've been left in the poo by a builder who cleared off with a staged payment and I'm having to do some work and planning myself. I need to lay waste pipes to serve a kitchen and utility room with loo at one end of the house and a bathroom at the other. Both will feed into an existing 110mm waste network leading to a septic tank. The house is to have solid floors. I cannot find any advice on whether I can lay the pipes just beneath the concrete sub floor in the kitchen; the floor isn't yet laid, and is presently awaiting it's subfloor on the earth. The older part (an old outbuilding) has an existing concrete floor which is approx. 8" below the finished floor level. Is it acceptable to lay the pipes under a concrete floor? I feel it's the only sensible answer. There will be a manhole at each change of direction outside.