Starting a Siphon
Siphoning Your Aquarium Water and Cleaning Your Aquarium Gravel
(The First Tank Guide)
First, place a bucket on a low stool or on the floor in front of the fish tank. You will use this bucket to catch the water you are draining out of the fish tank through the siphon.
If the siphon you are starting is attached to a gravel vacuum, place the wide end of the gravel vacuum in the aquarium, and rest its open end on or slightly into the aquarium gravel. If this siphon is not attached to a gravel vacuum, you will want to keep the end of the siphon in the aquarium several inches away from the gravel. Point the other end of the tube toward the bucket.
To get your siphon started, you will need to get water into the siphon tube.
Suck-Starting an Aquarium Siphon
Probably the easiest way to do this is to gently suck on the lower (bucket) end of the siphon tube while holding it above the bucket, but lower than the water level in the aquarium. As soon as the water gets past the edge of the fish tank and begins to flow down the tube, remove your mouth from the siphon and allow the water to flow into the bucket. However, some people think that this method is a disgusting way to get a siphon started (though the water in your aquarium should be no more harmful to you than it is to your fish). In these cases, there are other ways to get your siphon started.
Starting a Siphon with a Priming Ball
Some siphons and some gravel vacuums come with a priming ball. This priming ball is a soft, pliable rubber ball on one end of the siphon tube that can be used to start the siphon. To use one of these, you will need to plug the end of the tube near the bucket and squeeze the rubber ball. Air bubbles should be forced out of the siphon into the aquarium. If you release the pressure on the ball while keeping the end of the siphon closed, then the water should be sucked into the siphon and over the lip of the fish tank where it can begin to flow down into the bucket as soon as you release your finger. However, you will have to release your finger quickly after the water reaches the lip of the tank, because if air has a chance to get to the top of the tube, the siphon will not flow. If your gravel vac does not have one of these attachments, you may be able to pick up a siphon starter at your local pet shop.
Shake Starting a Siphon with a Flow Control Valve
Some other gravel vacuums have a valve in them that will allow water to flow one way, but not the other. The manufacturers of these recommend that you shake the gravel vacuum rapidly up and down in the aquarium to push water past that valve and into the tube. In this manner you can get the siphon started by just getting water pushed over the lip of the fish tank when it can start to flow downward into the bucket. I find that using this method always makes the aquarium unnecessary messy and often creates a mess. I also find that this is the most difficult method to use to get a siphon started.
Starting a Siphon by Immersion
Another option to get a siphon started is to lower the entire siphon into the aquarium slowly, making sure that you get all of the air out of the tube. Then you can plug the one end of the tube with your finger or thumb and lift that end out of the tank (being careful that the other end does not come out of the water) and lower it toward the bucket before releasing your finger. When you release your finger, the water should start to flow into the bucket.
Starting a Siphon by Pre-Filling
Similar in practicality to the immersion method of starting a siphon, you can start a siphon by pre-filling it with water from a tap or other source. With this method you need to carry the filled siphon tube from your water source to the aquarium, but that may not be too difficult. While I find this method more awkward than the immersion method, some aquarium owners find this much simpler.
The Real Rules to Starting an Aquarium Siphon
When you are starting a siphon, whether for cleaning your fish tank or for something else, what you need to do is get the water over the highest point in the siphon, with no air between the source water (your fish tank) and the high point. This can be accomplished by any of a number of means, and those outlined above are by no means exhaustive. These are some of the simplest, and most obvious ways, but if you don't like them be creative and come up with something... The point is to get the water "over the hump" so that water starts flowing and you can clean your aquarium.