I know that mold is definately leaking through some of the deep holes in my flat. You can see brick in the holes as well as space for air to travel.
Can pipes with cracks and holes behind them also leak contaminated air? I'm not sure what exactly surrounds the inner wall where pipes are passing but if its the same as deep holes then I guess it can.
When filling can you go right up to the pipe and make it airtight? in some builds I notice there is a small seemingly deliberate gap but if there were a leak above that would not be visible.