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There speaks a man who does it regularly.And I imagine you'd have to drill a 20mm hole right through to accommodate conduit, a bit OTT for 18 inches of 2.5mm cable, and generally you'd bash out a rear knockout in the existing inside socket back box so it's easier to use a smaller diameter masonry bit and avoid messing up the backbox. Always go slightly downhill from inside to out too and try to drill the very last bit without hammer action to avoid a huge lump of masonry falling off on the outside.