I guess that once Starship prototypes are complete they should be pretty weather- and dirt-proof. They should be perfectly sealed and stainless steel is well-suited to life outside (though sometimes I wonder about the tough conditions by the sea in Boca Chica - there must be parts or equipment that rust and get full of wind-blown grit ... anyway ...)
But the parts are stored outside, final joins take place in buildings without doors and those workers climbing in and out of the hatches don't look particularly clean.
How does SpaceX avoid problems with dirt, grit and sea salt getting drawn into valves and engines?