On Tue, 16 Sep 2014 14:01:16 +0100, soup
wrote:

My son has asked me to put a tap in to drain his trough (it is filled
with stones, plants sit on top of the stones and water).


Why not just drill a few drain holes half way up, is there a reason
for a need to have the trough so wet? that way you get the plants
being irrigated, I guess that is its wanted to have some water
sitting in the bottom