Sounds like a bad part of the power washer.
Gfci replacement plug power washer.
So with a 2 wire gfci plug and the washer sitting on dry ground it still tripped.
Works with all residential models.
It should be about 3 1 8 x 2 1 5.
Ar blue clean gfci replacement plug pw4221160 for electric pressure washers this also replaces part pw3084330 on older machines.
Gfci replacement plug power washer.
If i were you i would replace the cord with a 3 wire and just plug it in the garage gfci receptacle.
For pricing and availability.
Rv electrical adapter fits 30 amp male to 50 amp female with pull out handles type 10 3 stw 30 amp 125 v to 4 degrees fahrenheit cold.
4 8 out of 5 stars 1 858.
Tower manufacturing shock buster 15 amp 125 volt general duty 3 wire grounding straight plug.