Electrical – How to diagnose the cause of the washing machine shocking me

From all this, I conclude the following is likely:

• Only the outlet in the kitchen next to the sink is properly wired.
• All other outlets have hot and neutral reversed.
• There is no ground connection.
• Unexpected observed voltages (mostly 60 volts) are caused by stray capacitance.

I'll mark it accepted when I get complete confirmation.

Outlets need to have their hot and neutral corrected. Outlets need to be grounded or labelled as "GFCI protected" and "no equipment ground."

Fluctuating voltage from the actually hot line to true ground (the water pipe) is caused by current flow reducing the electrical resistance of the line. Voltage is otherwise high and stable for the capacitive currents as they don't induce enough flow.

There needs to be multiple compounding faults for you to get a jolt like that from the tub. The tub should be grounded to earth, but to give you a jolt, it would need to be instead bonded to one of the mains lines. Since your detector is no longer complaining, it must be bonded to the neutral line. While a bad situation, in normal use there are likely no adverse effects from this.

The other thing that needs to happen is a polarity reversal from either the power monitor or one of the plug adapters. For example, if you accidentally got an UK to Argentine adapter, it would appear outwardly to be for Oz, but in fact the neutral and active pins would be reversed. This too is bad, but also usually no adverse effects are apparent.

Now you have active mains power running down the neutral washer wiring, which inappropriately includes the tub. If the tub were properly grounded and active power somehow came in contact with it, the breaker would trip or the fuse would blow. Having been instead bonded to neutral, and now hot due to polarity reversal, two somewhat innocuous errors combine to become a potentially deadly combination!

First identify which device is reversing polarity. Looking at a wall outlet, with the ground pin on the bottom, both UK and Oz outlets have neutral on the right. Anything that switches sides should be destroyed. Not just thrown out, destroyed, as in render unusable.

The washer should be inspected and the connection to neutral identified and removed. It may be simply a wire with worn insulation that needs to be replaced, or something more intentional. It's impossible to say without inspection. The situation has not changed from before. While the tub bonded to neutral cannot ever be called "safe", as long as polarity is observed, nothing really bad should happen. You can still get shocked from this because the neutral and true ground are likely at different potentials, but nothing like the full 220v jolt you got.