Some my old discus friends had u-shaped pvc hung on the back of tanks with a stop cock at the tank top. Kind of a permanent siphon that is piped (or a hose) to a drain (to the sump in your case). The end in the tank had some kind of mesh or sponge cover to keep out large stuff & the flow can be adjust by how far you open the stopcock so your sump pump can keep up. No pump or filter is needed, just gravity...except to empty the sump well.
Do you have a laundry tub or other tap with hot & cold water? That & a hose for refilling, possibly to another u-shaped pvc to hook over the tank(s). Some had that part piped as well, the serious breeders with many tanks. It took my 1 friend 10 or 15 minutes to do 80 or 90% WCs on his 125g. Most had bare bottom tanks (no substrate).
I was always jealous of their set ups, I hope you can find an easy system. I thought about something similar at my previous house but I had tanks all over the house & a passive French drain (no sump pump, just a 4 or 6 inch pipe out to ? gravel dry well?). I also didn't want to drill holes all over my floors...but maybe for the discus tank if we'd stayed there.