sewerage systems.

[Timelord]

It would be pointless for an upstairs loo! lol. Don't forget any other drain connections and also the outside drains will overflow and this would need to be kept outside as well. Bricks are often porous over time and air bricks/grates are even worse If the sewer system is backing up due to flooding, then you could just knock the bottom off the outside fall pipe from the toilet. That would be cheaper and keep the crap outside. The problem with this type of sealing off design, is that the pressure will be great if the flood level is rising and you may wish to give some thought to the integrity of the woodscrews holding the toilet down to the floor! There's nowt like a good blowout!