Syphons (or Siphons) are one of the most useful but underrated and ignored aids for the kitchen gardener. We nearly always need more water than we can store for our choicest fruits and vegetables, and water is heavy stuff to carry very far. Syphons make it much easier to store more water and they also save us tremendous effort by moving it around automatically. For example, like many gardeners I have a small greenhouse which has it's gutters feeding a water butt standing outside. I used to fill a watering can and carry it inside to water my plants. Then I thought it would be better to have the butt inside to save effort, but there was insufficient space to house any decent sized butt. So I stood a small water barrel inside on top of a plastic crate and connected this to the butt outside with a syphon. Now it is always full of water and I can just reach over and dip in a jug to water my plants. If I use all the water in the barrel all I have to do is wait a few minutes and hey presto it's full again. And it saves carrying in all that water by the heavy can load from outside .
Of course as the main butt empties and it's level drops the small barrel becomes slower to fill and eventually stops but then all I do is take it off the crate and lower it and then it rapidly replenishes again. When rain comes and refills the main butt the barrel is set back on the crate otherwise all the water would syphon into it and flow away over the rim to waste. I realised that if I connected the main butt to another big butt receiving water from a shed's gutter then the second would keep the first filled and both would feed the barrel in the greenhouse. This worked well and as my garden is fairly level (it is Norfolk after all) I was soon connecting together all the other water butts. This was magic! By linking them all together with syphons I could now take water from any convenient butt and all the others would refill it. And when the rains came they filled each other up again.
This is the sheer beauty of syphons; because they automatically move the water for you with no effort you can store much more and yet take it out of any butt nearest where you need it. Even if you can only find space to have one butt by the main house down pipe you can connect it to half a dozen butts behind the garage and save all that precious rain that otherwise would go to waste. By connecting the solitary house butt with more butts secreted away somewhere else you increase your storage AND as you take water from the house butt the others will fill it back up again. Or they will fill up a butt anywhere else you want. And not just over small distances. My polytunnel is half an acre away from my house yet a syphon connects the butts by the house to a butt in the tunnel saving an unbelievable amount of water carrying.
All a syphon is is a pipe full of water connecting two containers of water. Water will flow until it is all at the same level, or until one end of a syphon is exposed to the air and breaks the seal. A syphon is not an overflow, that merely allows surplus water to flow and then only one way. A syphon allows you to fill and then draw on all the water in a butt, or a series of butts. And it does not require a tap or that you make a hole in the bottom of a butt as a syphon can go uphill over the lip and down again. Indeed syphons can go anywhere convenient even overhead as long as both ends are in butts which are at approximately the same level. Obviously if you are on sloping ground then to make the syphon work efficiently you have to adjust the heights of the butts. The high ground butt can be dug in or the lower butt raised - which is usually the simpler solution. Don't worry about trying too hard to get it right beforehand; as soon as you connect the syphon up it will soon show you whether you need to raise or lower the butts! Don't forget that water will always balance itself dead level in butts across the garden no matter how far apart they are.
To make a simple syphon take a hosepipe and weight the end so that it just hangs short of the bottom of your main butt and then take it almost anywhere you want, even uphill, as long as the butts connected are roughly at the same level. Weight the other end so it too hangs over the lip and just short of the bottom. To prime the syphon just use a hosepipe connected to the mains water to flush out all the air and fill the syphon with water, disconnect the hose from the syphon while keeping the ends under water and it will invariably work straight away. Of course you can suck out the air to prime it if you so wish instead but I don't recommend it! It becomes worthwhile to position delivery butts just where the water is needed, even temporarily. For example if your main butts are next to the house and you carry water from this to the vegetable beds then just connect up a butt there. From then on the water will be there waiting for you.
And a syphon will even deliver water to the plants for you. Immerse a long hose slowly into the water in a butt expelling all the air and then pull it out with your thumb sealing the end so it stays full of water. Lower this end till it is below the water level in the butt and remove your thumb, the water syphons out and can be directed where you want it. You can pull out as long a length of hose as you like providing the butt end stays near the bottom of the butt. An open ended syphon will empty the butt in only a short while, indeed if the butt is in a series the syphon will empty all of them! In fact accidental emptying of all the butts in a chain is one of the few problems that can occur. If any of the syphon hoses does get knocked down it is possible for it to empty the whole lot before you notice it. Thus it makes sense to secure the syphon hoses where they go over the lip of each butt. And as the hoses tend to kink at that point it is worthwhile slipping a piece of bent copper pipe over the hose to protect it at that point and this will also help to make it secure. The only other problem is that a hosepipe full of water can freeze and rupture in very cold weather - though I have never had this happen but I guess it would be a good idea to keep the hoses empty if the weather ever turns bitterly cold.
Naturally sooner or later a syphon will stop working for you. If you let the syphon end lie in the crud in the bottom of a butt then it may get blocked but this is unlikely unless a lot of leaves etc. fall into the butt. Usually it is that air bubbles have come out of the water and formed an airlock in which case a flushing with mains water from a hose soon puts it right. This only seems to happen when the syphon has not been in action for awhile as the movement of water tends to sweep away any bubbles that form slowly. Alternatively a pin prick leak will let water seep out or let air seep in which will similarly stop a syphon working. In which case pressure test the syphon with the mains, look for the leak, seal it with waterproof tape and then it will work again.
One slight drawback if not a problem is having the syphon hoses trailing everywhere. However these can be routed underground, overhead or even the 'long way round' so they are out of sight and harm's way. Any hosepipe will do the job but reinforced hose that does not kink or go flat on warm days is obviously best. If a flattened bit does occur (usually when the sun has heated it up and it is kinked over something) then warm the hose from outside with hot water while putting it under pressure from the mains to restore it's shape. This is rarely ever required as syphons are so simple they invariably work. Indeed I cannot express myself forcibly enough as to just how simple and convenient a syphon system can be, it really does make carrying cans of water any distance totally foolish. Move an empty butt to where you want your water, connect it with a syphon to a full butt and the water is soon there. Of course you may end up applying more water as it is easier to do so, but I doubt your plants or your back will object.