The first consideration before arriving at a cleaning solution it to determine how dirty it is and what is the nature of the contaminants.
If it's just dust and/or with a greasy film than a wipe over with a damage cloth (though I tend to use 303 Aerospace Protectant on the cloth) and a bit of time and small hands is all that's required.
Leaves and the like are easily moved with compressed air.
If there is an oil problem and this shouldn't be the case with newer cars then stronger chemicals are required along with a means to deliver water or a washing fluid to the area.
There are some good heavy duty cleaning fluids on the market if it's bad enough to need them.
I prefer steam as it's very effective and handheld streamers are cheap to buy but be aware you'll have the floor to consider when you move the car so lay down a protective layer of plastic or a big old floor mat is what I use then let it dry out and roll it up for another day.
I don't use a high pressure cleaner as I see it as an over kill in my opinion, certainly there are some jobs when they are ideal but it's not usually the case.
If I need a jet of water then I use a garden hose pressure sprayer like this as they are cheap around $16 to $25 or alternatively the one in the second photo as they give more options.
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