Hello; One caution that may not apply to your situation depending on the type of siphon tube you have.
When I siphon with the end of a tube into the gravel, I will pull gravel thru the tube and into the bucket. No matter how careful I am, some gravel exits the bucket with the used water when I empty it. As I have a septic system, I do not pour used tank water down a sink drain. Not only is there the risk of gravel colgging up drains, there is the introduction of tank detritus which can include things like snails or their eggs. I carry the old water outside to pour on the ground. I also use some of the water for houseplants.
You may have the type of siphon with a large end that feeds into a much smaller tube. I have a couple of those. They do not tend to siphon the gravel into a bucket. They are of limited use in a heavily planted tank as there is not enough space between plants to get down into the gravel. With few or no live plants that type should work.
One technique I use in planted tanks is to use a clear tube with an inside diameter somewhat larger than the size of the gravel. I siphon out the gravel with the water and pass it thru a typical fish net. I use a net that can be positioned on the top of my catch bucket. The net collects the gravel which can be dumped back into the tank.
Another technique is to position a quarantine tank (QT) under a main tank and siphon the water and gravel into that. I then use some clean extra gravel to replace that removed from the main tank. Eventually I remove the gravel from the QT and clean it. This has a couple of slight advantages. One turns out to be that the QT will get a regular dose of beneficial bacteria along with the gravel. This also keeps the taste of the QT water similar to that of the main tank for, by my thinking, a smoother transition of new fish into the main tank. (Note- the water in a QT needs regular changes with fresh water the same as any other tank. ) I used this method for a number of years.
A second benefit is an occasional fertilized egg will be siphoned out of the main tank into the QT. If the QT happens to be empty, I have had a few unexpected fry show up in the QT. I also keep some floating plants and snails in a QT which appears to keep the water conditioned (cycled) when no fish are present.
