Plumbing Bodge - will my solution work ??

Get a flexible rubber repair coupling the same diameter as the pipe you drilled the hole in. This coupling should have two band type radiator clamps on it. Purchase one more clamp identical to the ones on the repair clamp. Remove clamps get a knife cut coupling length wise, place coupling over hole, install clamps on each end, install extra clamp over spot where 8mm hole is. To use silicone to repair pipe the pipe must be clean and corrosion free. If you ever use a liquid drain cleaner or snake down drain to unclog it could displace silicone and leak. If not it will leak over time on its own. See web site below for coupling identification. Have repaired several drain pipes in homes using this method and it works. Next best is cut out old and replace but that should not be necessary. Good Luck.

If the pipe was dry when the silicone was applied it will probably work.The better way to do it would have been to use an epoxy putty that comes in two parts you mix by hand. This stuff works great.If it leaks clean it off and use the putty.

As a temporary fix,Yes it will leak again over time,

(a) you did not go through...(b)it is a drain pipe,not under preasure...I don't see any reason why you should have a problem....since I can't see I can't say for sure!!!

yes because there is no pressure on waste water drain