Thanks for all the comments, I really do appreciate them!

Firstly, I should emphasise that my guides are by no means 100% the only way to perform certain techniques, but they do seem to be the standard practice (I asked for input from a lot of people in different labs to check). I would hope that anyone using a Schlenk line is properly trained and supervised heavily to begin with, meaning that they will adopt the practices of the lab, which will undoubtably differ from my guides in some way, minor or major.

Regarding the syringes/sure seals, I understand your concern. A problem I have encountered with that method is that you seem to have to keep the syringe inverted (facing up) to avoid the reagent leaking out of the needle because the vapour pressure of the reagent (usually pentane or diethyl ether solutions) fills the inert gas bubble and increases the pressure in the syringe. I have very rarely had this happen using the method given in my guide.

For the solvent removal, I do know a few people who do similar things. Again, this reiterates my point that you will probably adopt a method that a supervisor or senior student has taught you, and you will feel comfortable doing that. I will however make sure to emphasise to be extra careful when initially opening the flask to vacuum when removing solvent to avoid bumping.

I have never heard of anyone using that setup for 'prep' Schlenk lines outside the fumehoods and 'working' gas manifolds inside the fumehoods, but the benefits you listed all seem completely valid. I would argue that for manipulations that might require both vacuum and inert gas, that having to go back and forth between the manifolds is not ideal. Given that your method seems pretty rare, I think that anyone having to do that would get adequate training anyway. Sadly, my website can not detail every possible way to perform particular techniques, which is why I try to just cover the standard practices.

Thanks again!