Yes water can get in.
Many SxS bbl sets have at least some small area along the 10ft+ or so of soft soldered rib where the joint has a pin hole in it or a very short section where it isn't sealed.

Water gets in,,but can't easily get back out through those tiny inlets.

Some bbls have 'weep' holes in the bottom rib up close to the FE lug. Some another on the short rib section betw the flats and the FE lug.
Some are a factory prep and others drilled there by someone doing a re-rust blue job.
The purpose is to more easily allow any water that enters to be drained back out.
Even then it takes a bit of care and time to get the water that enters to drain completely back out.

Sometimes removing the front sight bead will also help as some are drilled through the rib and reach the cavity.
At times there is a lot of soft solder under that area right at the muzzle and bead removal only leads to a blind hole in that position.

I usually use the weep hole(s) to drain and clear any water inside there.
I put the bbl set on a single wooden plug/handle inserted in one chamber. Then lock the bbl set near vertical in a bench vise.
The muzzle tilting over so the weep holes are bottom side and the set is muzzle down from vertical.

Carefully heat the bbl set w/a propane torch to make the water inside the ribs sizzle and steam.
It will 'spit' itself out of the weep holes when hot enough and some will want to run down the rib,,that's the reason for having the bbl set tilted forward.
I catch and soak up any that comes out with a papertowel. Having that hot water from inside the ribs run down a fresh rust blue job will discolor the new blue for sure if it stands there very long.
Keep heating, carefull not to get it too hot and compromise the soft solder joints. It's easy to do if you aren't really careful.
If you start to hear a creaking noise, back off with the heat! You are starting to get near that point.

Not necessary to get that hot anyway, Water boils and steams at 212F. Most SoftSolder melts at around 400F. No need to go anywhere near that temp.

When you think that any water has been made gone,,just let the tubes cool on their own.

Sometimes I will melt out the solder at the muzzle that seals up the end of the bbls. Especially on a set that has no existing weep hole(s)
That will give you an excellent drain exit.
On others I will drill a tiny hole thru the solder at the muzzle and into the void.
Some will not allow this (bbl keys, insufficient solder area) but it can work in other instances.
I still heat the set after bluing,, but muzzle down. Any moisture exits the open space at the muzzle.
It requires the soldering back up of the muzzle but that's simple enough with an electric soldering gun