Hi all, I'm looking to replace the plastic header tank on my 2005 sti with one of the metal ones. Couple of questions, though I think I already know the answer to #1

1) can I get away with swapping the tanks over without a full drain and coolant change? Maybe a clamp on the hoses and top up with water?

2) is it worth/safe using a liquid gasket to compliment the rubber gasket between the body and lid of a second hand tank?

Thanks all