I work in a government agency building, less than 10 years old, built to some kind of 'green' standards.
When I am in a men's bathroom, either at a urinal or a commode, when someone flushes a toilet, either in the men's, or even in the women's next door, it sounds as if water is being flushed down the floor drain at the same time. (In fact, it sounds like the flushed waste is going down a drain, although that is (obviously) not true.)
Why is this, and what is happening to cause this?
Per a comment: Yes, the sound is coming from a floor drain
(It happens in all bathrooms on all floors of the building. The audible whoosh/splash sounds immediately following hearing a toilet flush. It's easier to hear in 'our' bathroom when a person in the other bathroom flushes, but it also happens when our toilets/urinals are flushed.)
Best Answer
The sound you hear is the “primer” releasing a “squirt” of water into the floor drain. The primer is activated when a nearby water valve is activated. In your case it’s the urinal valve.
The floor drain has a trap that blocks the smell from the sewer lines from flowing back up the sewer lines and into the room and building.
Primers are placed on drain lines and traps because they do not get a regular flow of water to keep the trap full.
Because you didn’t complain about a sewer smell, I know your primer is working.