Sounds like you got it working
When you start the siphon, with the cap on, it flows REALLY fast. But that is what sucks it down and uncovers the inlet. Once you take the cap off, the drain slows to only what is needed to keep the tank/bucket at level. When the tank level rises a bit, more water will be forced through the pipe and down the drain, if tank level lowers, the flow slows. The drain should set itself to flow the same as what your return pump is putting back into your tank. The will ballance and that's what's needed
Glad to hear we have success