Recently moved into a house with a garden igoo - one of the orb type ones with plastic/pvc cover. It’s nice to sit in when it’s slightly cold but sunny. Question is how on earth do you keep it clean? Company instructions say plain water only. I’ve blasted it and wiped it over but it still looks grubby. I asked my window cleaner would he clean it but he declined. Any ideas/experience? Any companies that clean these type of things?