Siphoning happens when things heat up too fast, so the water/steam is much hotter than what is in the jars. Siphoning also happens after canning IF the steam is let off and doesn't subside on its own, do not release any steam after canning, just let it cool naturally. Siphoning can happen when it is naturally cooled, and opened quickly, and jars immediately taken out they will continue to send liquid out near the lid. So that is three ways siphoning happen, two of them due to differences in temperature and one due to letting off the pressure.
When you begin pressure canning, you turn on the heat but the steam vent must be left open and shooting out steam for 10 minutes before beginning. THEN put the weight on the canner, bring it up to pressure, and get the weight to rock nice and slow at 10lbs, by slightly reducing or increasing the heat below. Once it is stable, you begin to time it. At the end of the time, turn off the heat and do not remove the weight until there is no steam making any sound at the steam vent w/weight. (this takes about 40 minutes) THEN take the weight off. THEN open the canner slightly, just cocking the lid over it, to let it sit for 10 minutes. After 10 minutes remove the jars from the canner and put the jars on a towel with no breeze/fans. Let cool naturally overnight or 24 hours before checking the seals.
This really should reduce or eliminate any siphoning.
I'm sorry this is so long. I hope it is clear. Please ask questions if I wasn't clear.
