I've found with washers volume of water is more important than the pressure, less likely hood of water getting in connectors & removing decals. Mine is more commercial so it is plumbed in, combined with on demand hot water I can add warm water.
Good quality foaming gun I lay the foam 1" thick & let it soak in. Using the Hi volume nozzles you can really control the water fro cleaning the inside & areas where you don't want spray everywhere.
I'm gonna try & hunt down Slick Products in Canada, NMK's link looks interesting & when the concentrate is mixed down you get 16 gallons. Always game for trying new cleaning products!