This is the most common Oring needed on a paintball gun. Often called a tank oring or a bottle oring.

Front Bolt Oring on the Tippmann 68 Carbine Diagram - Does NOT create a static air seal in the gun. Leaks you hear don't come from here.
Tank to ASA Oring on the Tippmann 98 Custom ACT Diagram
Tank to ASA Oring on the Tippmann Model 98 Diagram
Tank to ASA Oring on the Tippmann 98 Custom Pro Diagram
Tank to ASA Oring on the Tippmann 98 Custom ACT Pro Diagram
Tank to ASA Oring on the Tippmann 98 Custom Platinum Series ACT Diagram
Valve Oring - Bottom - Small on the Tippmann 98 Custom Platinum Series ACT Diagram
Tank to ASA Oring on the Tippmann 98 Custom Platinum Series ACT Pro Diagram
Tank to ASA Oring on the Tippmann 98 Custom Platinum Series Ultra Basic - Non ACT Diagram
Valve Oring - Bottom - Small on the Tippmann 98 Custom Platinum Series Ultra Basic - Non ACT Diagram
Front Bolt Oring on the Tippmann Pro-Carbine Diagram - FA-17 on some diagrams.
Tank to ASA Oring on the Tippmann A-5 Basic Diagram v2 2009-08-06
Gas Line to Tombstone Oring on the Tippmann A-5 Basic Diagram v2 2009-08-06
O-ring Tank Valve - Transparent Urethane on the Tippmann Cronus Diagram (1 of 2)
Vertical Handle ASA Oring on the Tippmann Crossover Diagram 2012-06-20
Tank to ASA Oring on the Tippmann Crossover Diagram 2012-06-20
Front Bolt Oring on the Tippmann Pro-Lite Diagram
Valve Housing Cylinder Oring - Large on the Tippmann Crossover XVR Venting Regulator ASA Assembly Diagram
Tank to ASA Oring on the Tippmann X7 Photographic Large Diagram
Tank to ASA Oring on the Tippmann X7 E-Grip Diagram 2007-11-26
Tank to ASA Oring on the Tippmann X7 Phenom Mechanical Diagram 2013-11-29
Tank to ASA Oring on the Tippmann 98 Custom Platinum Series RT ACT Parts Diagram
CO2 Cap Oring on the Tippmann TPX Diagram 2008-12-02
Tank to ASA Oring on the Tippmann X7 RT Diagram
Tank to ASA Oring on the Tippmann X7 Phenom Exploded View v3 Diagram and Parts List
Tank to ASA Oring on the Tippmann 98 Custom Diagram - Push Sear Style - Non ACT 2006-08-06