In the automatic car wash there is a package that sprays the undercarriage as you drive into the main car wash. Just drive slow thats what i do.
Of the two bays, the one on the left (your left as you're entering from the back, facing towards the street) has 2 lower stationary sprays that start as you're pulling into the bay; they clean the wheels and maybe part of the under carriage. I *think* the bay on the right has a direct under carriage spray... I'd try that one first.
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