It depends on your return pump size. A single 1" drain is typically rated for around 600 gph. If your return pump, after accounting for head pressure loss, is pumping 600+ gph up to your tank, then you could certainly have a problem. A slightly larger drain size compared to return line size allows for more passive, free draining of water, and a little margin of safety if the drain becomes coated or partially clogged over time or plugged by a snail or hermit. If possible, I'd recommend increasing the size of your drain line, or have multiple drains.