Plugging a stone sink drainage hole

I have an old limestone sink with 2  drainage  hole on it's vertical walls. I am going to try to grow a miniature water lily in  the sink. 

I have plugged one hole with a wine cork, the other hole is partly plugged with a champagne cork, but is still leaking. 

Is there a clear substance, I can seal round the cork with, that is easily removable if I change my mind and want a bog sink?

I think the sink was original used at the bottom of a downpipe, I think the water then drained from the sink/trough into the street from this hole in the front.  The water trickling out has worn a groove in the stone over the many years.  I am trying to block the hole without leaving a load of modern day gunge showing round the hole.  (Apologise if this doesn't make sense to anyone.)

Or if you don't want to gunk it how about something like a cistern blanking plug.

They fit over the hole with a threaded on to the other side and a nut on the back, so it would depend how out of round it was.

A picture paints 1000 words http://www.screwfix.com/p/fluidmaster-blanking-off-plug-white/65267