"Neighbours over the edge"... would that be a high edge then, with certain death on the other side?

Either way that's just terrible, poor neighbours.

Washing a car with a little knapsack is terrible too though... I think I would lose the will to live.
Personally don't like washing cars, takes too long, too much like hard work to me and where I live the results probably last the 10 seconds it takes me to drive down my lane.
I don't have neighbours too near though, so I will focus on the finer side of car washing... power-washer upgrades: maybe an Impreza flat-4 on the first one and a turbo and supercharged LS1 on the second yoke? -proper Junkyard Challenge like...
Why can't they just invent and use car paint like the new generation nano-tech building paints... where the dirt just falls off and cannot stick as it is sooooo smooth? Wash the car once and forever shiny
If there is no space, no electric, no tap and a constraint on noise... then I guess the knapsack seems the only "solution" -- However would you not nearly rather drive to you nearest garage and wash it there?