Single Main Drain

[Throwaway543]

I have two main drains in my deep end, but one of them is dedicated for the waterfall and uses a separate pump. My understanding is that you have two drains for safety and that the waterfall was probably retrofitted and stole one of the drain lines. As I replumb the pool this spring, should I plumb it back into the main circulation system? If I wanted the waterfall to still work, is my best bet just adding a diverter valve on the pressure side?

[Teapot]

Yes, sounds like the best option for minimum work. I usually plump main drains to use as inlets as it bring hot water into the lower parts of the pool and can re-float some dirt to mix and get skimmed out. This is via 3 port valves so they can also be used as main drains when and if required.