I used to use a dual system where the water but gravity fed the system but if I plugged in mains pressure then itr would activate the sprayers... it worked well, every morning I'd go down the greenhouse, put the hose into the waterbut and start filling that up, go into the GH, weed, sideshoot, harvest etc and wash out the filter unit, head off round the garden to sort out anything else that needs doing, then when the waterbut was full enough I'd plug the hose direct to the filter unit, which set the whole greenhouse into overhead spray mode.... let it have a 30 seconds or so of that then turn off the hopse, reattach to but to the fitler and it sits there dripping away happily for the rest of the day.... no need for any electrics :-).... A friend of mine has a similar system but permanenetly plumbed with switches and timers adn it basically does what mine does but automagically.... but he built the box himself and there's a toilet ball-thingy in the but with a microswitch on it.....
chrisc
