listen,... you need a petrol pressure washer, it can feed from a tank if need be , but it...s not essential
connect it to the customers tap, and crack on...
i do it all the time in summer,... make sure you clean it thorough and clean all the mess away afterwards...
you dont need two people at all,... and if you keep your prices at a reasonable rate that you are happy with, you will get plenty of work....... and dont forget to add 25. 35 pound for sanding.
its easy and enjoyable... a bit mucky but its not something we should be bothering abou bit of muck,