So, I feel like I've picked on Solemn's writing a couple of times now, and haven't given her a chance to reciprocate. Plus, the wife's out of town, and I'm bored and the kids are asleep. So:
Tap Whistle hated to work in the rain. It loosened the black from the streets and buildings, and made the manhole diving unbearable. You didn't want to get caught by the Plumbers when it was raining. If you tried to run, you'd just end up slipping in the black runoff. After a couple of hours of rain like today, the sewers would be full up to your knees.
It also seeped into the battery jars, and the top layer of grease would short out the 'nodes, leaving you no voltage. Anyway, you didn't want to get caught with a jar if you could help it, or else you would be charged under the Tesla ban.
The rain made it too noisy to scope the street for audio, too. Not that sound would do him any good at the machine point he planned to monitor today, not from the topside.
Whistle wouldn't even bother on a day like today, except that he had a rare motivation, a paying customer. It seems that several of the local "plumbers apprentices" had named him as the best when the norm had come around looking to hire a hole diver. He was even more nervous than Whistle, and it made him laugh inside to think how paranoid the norm was about getting caught. Whistle wasn't worried, why not get paid for some of his fun? He suspected he wouldn't be able to get the message anyway.
Whistle didn't actually have to pop any holes today, so he had left the crowbar at home. This junction point was big enough that it had its own housefront. Most of the major machine points had a little house-like building on top of them. The house part was little more than a single-story box with a front door. Inside was just some storage, a wall of valves that ran below, and the circular metal starcase that led down to the workroom. Whistle had a key that he had traded for, that would open the front door. It was a simple warded key, not one of the newer pin tumblers. Those were not thought to be reliable enough, though the lockers considered them more secure. That was about the extent of Whistle's lock knowledge, which he had mostly picked up from trade pamphlets and a couple informal demos from the lockers at the meetings.
Whistle checked for any of the copper-clad Plumbers carriages on the street before letting himself in the door. Once inside with the door closed behind him, he headed straight downstairs.
At the bottom of the stairs, he stepped right into the water, feeling the cold grip on his calves, dragging at his pant legs. The rain was seeping from the walls, and dripping from the curved ceiling, between the bricks. Parts of the sewers under the city went back to Roman times, though not under a machine point. In a machine point like this, they had typically been dug down two stories worth, and rebuilt, like a mini Underground station in the dark. They didn't carry any trains though, just pipes and conduit.
Whistle's target today was Lloyd's. They were an old user, so they still mostly used the pneumatics. Usually, only the newer users used rods, because they didn't have as many feeds to convert. There were a couple of exotic hydrolics in town, used in local building carrys, but that was only the standard in America. You wouldn't find a hydrolic in an official machine point. Whistle had a few catalogs from Edison's Hydrologic Manufacturing Company, describing what they had over there.
He light the gaslight, and pulled a couple of books from his pack. One was the city feed directory, which would give him the numbers he needed to check for. Customers would use these to look up the endpoint and route. The other was a stolen PCL manual, which would give him the stamped numbers he would need to read off the pipe he wanted. He looked up the machine station he was in, and found the list of Lloyd's serials. Lloyd's had mostly low numbers, they had been around longer.
One challenge was that, through this particular station, Lloyd's had no less than 21 tubes, too many to monitor at once. Whistle knew to check which switch they went to, though. And only one switch down here lead to the destination he was supposed to watch for.
He found that only four of the tubes went through that switch, so that was the set he would have to watch. From his bag he pulled a set of loadstones and reed flags.
Carefully, he found the places in the middle of the tubes where the plungers would have to cross. The places where, when the plunger went back and forth, it would flip the flag one way and then the other, giving him a visual means of watching the bits. Down here, you could use a horn to listen to one pipe, if you only had one to watch. Well, maybe two. He had heard of one blind kid that could do two at once.
For a lot of beginners, tapping by ear was easier. Especially if you were used to decoding by ear at a legitimate endpoint anyway.
But that didn't help if you needed to watch four. Whistle set up the reeds so that the reflective sides were to the right, where the gaslight was. Once the plunger started going, the flashes would let him read the message right off the pipe.