I reinforce ckessel's comment - I too researched it quite a bit. There's a point where it's clear that unless you pickup and drive without stopping out of the state, you've taken possession. So the bathroom break could be considered making use of California's amenities, and subject you to sales tax. In practice, you pay it. Period.
Got my dander up enough to send the folks that collect California's taxes a suggestion that they're killing an excellent tourism industry. Let's see - draw families to California with enough income to think that buying a $100k car AND picking it up in California to drive home is a reasonable thing to do. Think those families might stop by a theme park in SoCal, or see the sign in Hollywood, or do other touristy things while they're in the neighborhood? It's a start to a beautiful and classic American vacation, and it starts in California. CA could be getting an outsized chunk of the tourist dollars spent by those people, and instead they get nothing.
I'd like to pick up Model X in Fremont and drive it back to Oregon. Without a simple change - I suggested they implement a manufacturer issued 30 day temp tag (so only California manufacturers of vehicles can issue the temp tags - not dealerships, as part of picking up the vehicle at the factory). CA gets $50 or something worth of short term temp tag plus tourist dollars as people look around before driving home. Then the rest of the system stays in place just the way it is.
Ah well.
