Hi Jeff,
That is indeed a start-up/warm-up bottle you're looking at in the pic. I built a "docking station" on the front of the engine and it plugs into that for use. We use a Parker hydraulic quick-connect setup. In the pic, we just wanted to fire it to check for tranny pressure so we didn't want to run any nitro. The main fuel tank was empty (we didn't want to fill it) and the running engine would have been spinning the pump dry, so we just removed it.
The bottle is a CO2 paintball tank that I've removed the end from and tapped -8. I put a fill cap on the other end with a valve in it to vent so the vent can be closed (we can lay it down in the back of the tow rig and not leak) as well as a valve to shut it off above the quick-connect.
The bottle will run the engine for about 2 minutes before it runs out. The idle nozzles have been sized so that they deliver the right amount when just feeding from gravity. I think they are currently matched .028's. When warming up at the track, we go through one bottle checking the timing and trans pressure. We refill, discuss the state of things, fire again and then switch over to nitro to adjust idle and stage volume.
When switching over, we open the regular fuel shut-off until we hear the sound of the engine start to change. The regular system starts back feeding into the warm up bottle and we turn it off and disconnect it. What's left in the warm up bottle has nitro in it and can't be used again for start up.
When the weekend is over, I always rinse the warm up bottle in the parts washer and poke up into the quick connect to allow solvent to wash through the fitting. Otherwise, methanol gets trapped in it and it will rust up. I have used brass quick connects before, but lately we use steel and just take care of it. Also, quick connect fittings have an o-ring in them. The o-ring can swell up from nitro and cause you problems. So, we replace ours every season.
I really like the warm up bottle approach and in my opinion, it's the safest way to start up when running nitro. I think if a person is running more than 50% or so, they should figure out a safe way to start the engine. Cranking a motor over with nitro (even a little bit) in the cylinders can be deadly. There are several different ways to do a system like this that are fairly easy. Mine wasn't the simplest to put together but it's very easy to use.
Spud