Pipe Dope and Fittings Not Dry

[Jdbs3]

I'm replacing a boiler drain with a gate valve with one that has a ball valve. I will isolate the boiler by first closing ball valves on the return and supply side of the boiler (yes they will also be replaced after this boiler drain). I may or may not need to replace the nipple between the boiler and the current boiler drain.

Two questions:

- Will closing these 2 gate valves cause a vacuum such that minimal to no water will come out when I remove the old boiler drain? I hope so, so I don't need to drain the whole boiler.

- If not, then can pipe dope be used in the presence of water when I am switching out the boiler drain, and possibly nipple? It might need to be a quick change to lose minimal water from the boiler.

Thanks

 

[Kreemoweet]

What you're hoping for doesn't work on water heaters, so I see no reason it would work on a boiler.
Why not drain first? Water's cheap, y'know. Most pipe dopes are oil-based and unaffected by water (good thing, too!).