Cash is vital in Phasmophobia, as without it, you can't purchase equipment, and without equipment, how can you remove ghosts? We highly doubt asking the ghost to vacate the premises will go well in your favor. In reality, they'll just call another Paranormal Investigator out who can afford to do their job! To gain some extra money, you can take photos of evidence using a Photo Camera, and one such evidence is Dirty Water? But how can you get dirty water in the sink in Phasmophobia to earn that extra money?
How to get dirty water
If you have the objective to find some dirty water, well, it's going to cause a tricky situation at best, as Dirty Water happens as a result of a ghost being pissed off. On the odd occasion, if you're fortunate, if the sink is turned on and the ghost enters the room, it could turn dirty, but the chances of it are meager, so if this is your objective, don't rely on this method. Oh, and remember to bring along your photo camera and some film!
Once in the haunted location, hunt for some sinks; once found, your main objective is to get the ghost extremely annoyed. There are plenty of ways to do this, such as switching on all of the lights staying in one group, to making a lot of noise.
One of the fastest ways is to talk to the ghost and ask it questions without using a Spirit Box, call out its name, start firing out questions, but do this near the sink, as you want it to be pissed off and coming for you. Once your ghost friend is angry, wait for it to appear, or listen for it to make noise, and then switch to your camera and get ready to take the picture. Make sure the whole sink is in the picture, with a plain view of the dirty water. Then run like hell and hide somewhere! As you've just pissed off a ghost, what did you think was going to happen?