I don't have an opinion about power cords for the devialet but I can report that a separate ground did wonders for me.
I built thick copper mesh, about 1m square and buried it more than a meter into the ground ,in addition I used 2 solid copper ground rods going additional 15 meter into the ground. I also. connect it to water line. All joints are crimped and welded. In addition I keep the ground moist ( irrigation) For me it's by far the best twerk I ever found. I do it for years now, ( every time I move apartment or house) and I always amazed of the positive deference. I know it's not easy tweak , specially in apartment with neighbors
I built thick copper mesh, about 1m square and buried it more than a meter into the ground ,in addition I used 2 solid copper ground rods going additional 15 meter into the ground. I also. connect it to water line. All joints are crimped and welded. In addition I keep the ground moist ( irrigation) For me it's by far the best twerk I ever found. I do it for years now, ( every time I move apartment or house) and I always amazed of the positive deference. I know it's not easy tweak , specially in apartment with neighbors