We use multi exit clearing boards, (sometimes called Canadian clearing
boards here in the UK) and find them to be very fast. However they have
one drawback, if they are left on more than 12 hours under the supers
the bees simply crawl back in through the openings (this is only natural
since if a bee can get out through the opening it can get in through the
opening)
There seems to be a period of "learning" since up to about 12 hours they
clear the supers almost completely (perhaps a dozen bees left) Left on
for a day and a half they are 3/4 full of bees again. Anyone had similar
experiences with these boards?

Alan Riach
Bathgate (The Wild Boar Wood)
Edinburgh