I made a Manometer to check Crankcase vacuum. Its just a U-shaped clear tube fastened to a board with one end connected to the dipstick or other connection to the crankcase. (Above the oil, of course.) There are directions in the old K-series manual, at least there is in my copy.
The reason there is a pulsing in the crankcase is the piston. When it goes up in the cylinder it creates a vacuum and when it comes down it creates a pressure. The idea of the crankcase breather (reed valve) is to maintain a small amount of vacuum in the crankcase so oil won't be forced out through the seals, gaskets and governor bushing every time the piston comes down the cylinder.
If you make your own manometer, put some kind of shutoff valve in the line to the engine. I made mine with 1/4" clear tubing from a pressure washer soap injector, so I just used a 1/4" fuel shutoff valve.
You need the shutoff. On single cylinder engines, when you hit the starter, the first time the piston goes up in the cylinder it can suck all the water in a 1/4" hose into the engine. After it starts, the change in pressure is happening so fast they almost cancel each other out. Just connect everything, make sure the shutoff is closed, start the engine, open the valve and read the difference in height of the water with a yard stick from one side of the tube to the other.
If you plan on keeping water in the manometer, its a good idea to put a little anti-freeze in it. it also makes it easier to read.