coolant issues

A week ago I drained the coolant from my truck, removed all the LPG kit, replaced the thermostat for a 78 degree one, replaced both rad caps for OEM 0.9 bar items, added the little t-piece so I can pressurise the system, pressure tested and fixed all the leaks, replaced any dodgy hose clips then refilled the system. I then ran the engine until the fan kicked in twice (which it did) and let it cool. Once cool I topped the system up and filled the plastic reservoir thing up to the full mark. Each time I took the truck out I have been topping up the rad cap under the passenger seat, only a mouthful each time but as I'm still doing it I thought I had a leak somewhere.

However today I noticed the plastic reservoir is above the full mark where I previously filled it to. What does this mean?

Get it all burped of air again, warm it up, take it for a little gentle drive round the block, cool it down 100%.... etc etc until you get no air gap under the metal cap.

Then take it for the thrashing of its life.

If it purges a load of coolant into the header tank then more than likely the head gasket has gone.

I was afraid you would say that! Whats the best way to burp it? Just squeeze the pipes? Engine running? Cap under the passenger seat off?