A/S as you see is like a snorkel, it helps keep the liquid CO2 out of the gun. Just so you know it needs to installed by an airsmith (you can't just do it). And it needs to setup for the gun it's going to be used on since as the other picture shows it could at as a siphon if not installed right. The anti-siphon is just for your tank, filling the tank as no effect on the A/S. For HPA you need a HPA/compressed air (same thing) tank like this Crossfire
. Like i said before HPA/compressed air/nitrogen can all be used in the same tank, you can not put compressed air in a CO2 tank just so know.