priming 300tdi

pipes from the fuel pump to the injectors have been off. Engine has also been drained down.

I saw a video that suggested breaking the nut at the injector, turning the engine over until diesel starts to spirt out at the top of the injector, then tighten the nut. This, along with pre-filling the fuel filter will help prime the engine.

How do you stop the engine starting when doing this? Is it the stop solenoid connection you need to remove?

Yes, pop the thin white wire off he terminal but if you are just priming it you should be able to do that via the lift pump on the drivers side of the engine up to the FIP then it really doesn't need much to get the high pressure pump to work its magic.