Making an analogy between a plumbing system and an electrical system (pressure in PSI is volts and flow in GPM is amps), find a few "normally draining things" in your house, fill them with a known quantity of water and time them till they empties.
For this test, I remove the stopper
Google (Search Results)
(if present) at time = 0 because I don't know how much these sink stoppers reduce the draining GPM (which is about 4 GPM).
I used to use the presence of a small whirlpool to decide if a sink is draining properly, but now I use the time to drain and
You are looking for high resistance (low GPM) in your electrical/plumbing circuit.
Now. . .to complicate things:
Let's say you have a 2" ID drain and there is a clog 20' distant. It'll take about 3 gals into the pipe before you notice any trouble, then you'll see a reduced or zero flow rate.
There is no analogy for this in electrical circuits because the wires are always full of electrons. Voltage just causes them to move and the movement is the current.
For checking (vent) pipes from the roof or toilet drainage you'll need a GPM meter - it's about $30 IIRC.
You can get about 6 GPM max from a garden hose on city water and there needs to be an air space between the pipe inlet and hose/meter output.
Once the pipe is full you want to measure the GPM that the pipe can drain without overflowing, and you'll need known good vents/pipes for comparison.