will this work? Siphoning from tank to tank

[hillegom]

I am not sure if I have everything right. But I think you are pumping up from the basement to the higher 3' tank and then syphoning from that to the new 6' tank, where it will overflow back to the basement sump.
If that is the case, then in a power failure, the syphon breaks, no longer flowiing from the 3' to the 6' then back to sump in basement.
Then you must have a means to recreate the suction from the 3' to the 6' when the power comes back on. If it is a U tube, they don't start themselves. That could be done with a cheap powerhead. You use the suction from the part that would normally carry air before it mixes with the outflow.(fresh water tank)
But I agree with the other posters about getting a bigger sump pump. Less hassles and worry.