Leaking Air Venturi tanks

[Tin Can Hitman]

Greetings fellow Airheads
I have several AV tanks, including the stock tank for my Sig Virtus, that are leaking from the fill nipple.  I pump so I'm suspecting dirty air from what I've read.  I replaced my filters but the tanks all empty within 24 hours.  When I put the slip covers on they shoot off the nipple like a friggin rocket!  I've looked at a lot of info but am a total noob with PCP/HPA.  Don't know anything about dismantling / repairing regulators and such. So now my decked out Virtus and modded 850 sit in their racks until I wrap my head around this.
On the brighter side, I recently grabbed myself a Ruger Impact Max Elite from my local Walmart for $160 and am in LOVE!  I'm mostly a 20 / 30 yard shooter so the included 4x32 scope is just fine.  This gun really is quite accurate and the power with 14.3 lead is so far more than enough for my pesting needs.
Any thoughts, ideas or magic wands?

[RichH]

With the tank empty, unscrew the fill nipple, clean it out, remove and replace the o-ring. Off hand I think it will be a -007, but not 100% sure.

[Back_Roads]

 Here are the basic parts, some do not have the spring, and use air to close.

[Tin Can Hitman]

Thanks so much for the input.  I was worried about removing the nipple and have tiny parts fly everywhere.  So far so good; gonna go pump some air