Can you really breathe through a submerged toilet? In the movie kingsmen, (spoiler alert) a room is flooded with water. To stay alive, most of the characters stuff tubing into the available toilets and breathe through that. (you can see them in the picture below in the background)

I wonder if that's actually possible. Luckily, there was an immediate explanation given by another character afterwards for people like me:

For those of you who are still confused, if you can get a breathing tube through the U-bend of a toilet, you have an unlimited air supply. Simple physics... worth remembering.

Except that this explanation didn't make much sense to me. Is this a case of simple physics or rather Hollywood physics? If the room is full of water, each toilet will act as a drain. The trap (which I guess "U-bend" in the quote refers to) will not act as some kind of barrier. The water going down the drain will displace the air in the plumbing. Making it impossible to breathe through the toilet.

I'm not exactly into fluid dynamics, but even if there was some air left in the plumbing , wouldn't it be extremely difficult to suck it out, because of the stream of water that surrounds it due to the Venturi effect?
 A: For a complete answer, see this identical question on movies stack exchange. However, the brief answer is:
P-Traps and vent pipes.
If the water from the room were to make the toilet act as a drain, there would still be air from the vent pipe coming from above, as the water would flow downwards. It would be a nightmare trying to get the tube into the correct position, but possible.

A: As depicted in the movie it's possible but complicated. The drains serving the toilets would have to be blocked and the vents serving those drains also blocked and pressurized to maintain the water level on the outlet side of the trap.
A: If the pipes/tubes are long enough, wide enough, and you can suck hard enough, it should work. So whether it works depends on a number of factors. 
The water in the room fills the toilet and pushes water down the wastepipe. If there is too much water flowing through the drain completely replacing the air in the drain, then there is little chance. 
A: Yes it is possible there are a lot of reasons so we are going to be here for a while
First for the water to go down in those toilets there has to be air pressure from both the outside the toilet and the INSIDE of the toilet meaning there is both let's say a water tank and an air tank inside the toilet. Now that we have established that there is indeed air inside the toilet lets move on
Now you might ask. Is the air supply really infinite? Well yes coz the air does bot come from the inside and outside as I write above
Third, although it's hard getting the shower pipe through the water tank into the air tank if you actually manage to do it then you will actually have a refillable air tank. In other words infinite air supply
