Do water heaters have a check valve?

I recently teed into the cold water supply line that goes to my water heater. I planned on supplying another fixture in the garage through this tee. I started wondering, because the tee is so close to the inlet to the hot water heater, when I open up the new fixture will it draw hot water back out of the tank?

It's not likley...

water heater

NO, but the water in the line above the tank will usually get hot because of convection, so the initial water, at least, will probably be hot.

Thanks HJ. I kind of figured/hoped the water was just getting warm from convection.