[Steve175]

Originally Posted by Rover88

This is a giant nope. Never ever try to use two pumps unless they are both leaving the same sump and are for redundancy.

If you rely on two pumps they will never perfectly match up, and you will either starve one pump and run it dry, or overflow your tank.

This. NOOOOOOOOOOPPPPPPEEEEEE!!!!
You need a bigger sump and to raise the lower of the 60G [or move them closer to the sump]. Big volume = stability, so it will be worth the trouble. The complexity you suggest is a non-issue. Gravity works and remains constant over time [unlike pumps]. I have a refugium draining This thread has been split. into 2 DTs and 2 surge tanks draining separately into each DT with both then draining into the sump; separately I have a frag tank draining into the same sump and again separately [all via a manifold] a cascade of a SW mixing tank into a tank of dark LR [cryptic zone] into a 6 foot DSB and then into the sump. and I added a small mangrove tank on the manifold draining back into the sump lol. The displays are 250G, the frag and refuge 220 each, and each cascading tank is 150 [and the mangrove tank 30G lol]. My sump is 300G and still overflows if the display pump loses power [admittedly, displays are remote at about 20 and 40 feet to the adjacent living room with 2" drains and 1.5" returns]. The sump does not overflow if either the frag tank/cascade pump/reactor pump/skimmer feed/mangrove pump loses power or if the surge tank/refugium pump loses power - but only because the sump is large. Think about the volume that each tank will drain until the overflow stops plus the volume in the return pipes [make sure you drill a siphon break in all of the return lines]. Cascading tanks as you plan at least double that volume. Plus the column of water in the return pipes from the pump(s) will return to the sump. I am not trying to discourage you. I love my system. But only because my sump is the largest tank in my system. A rubbermaid 150G might be an economical perfect solution for your system - or a used 180G tank, or a big sump from someone getting out. Or build one [I have done all 4 over the years lol]
My $0.02.