Fill the reservoir, but not to the very top. Start the car, and have a buddy turn the wheel lock to lock. You can watch the fluid level, which should drop. Top if off as he turns it a couple dozen times.
Usually it overflows if you fill it very full and then go for an aggressive drive...the cap isn't airtight but I'm pretty sure you don't want to bleed with the cap on. It may just be you had a lot of air in the line and with the cap on it forced fluid out (when you hit the bump stops at steering lock, the pressure increases a lot).
