Thanks everyone for your suggestions. The pool company we hired, "Total Pool Care", wasn't exactly "total". My husband bought an immersable mini camera. We snaked it down the pipe toward the main drain. We saw the blockage about 5 ft down, at the bend. Palm debris. We bought a plumber's snake, but found it too slow. We rented a powered snake and had it cleared in 15 minutes. Thanks again for the tips.