Fizz71
FragSwapper
I ran a 105g tank once with 4 rubbermaid tubs as my "sump"..they were in the basement but the concept matches your 2 tanks.....
Water came in to #1 which was connected to #2 via huge bulkheads at the bottom of the sides of both tubs. Then I had a bulkhead on the bottom of the side of tub #2 and pvc coming up and over the edge of my smaller tub #3. Gravity pushed the water up and over and on pump failure #1 and #2 would level out to the height of the pvc.
FYI tub #4 was above the rest as a fuge...small pump pushed water up to it and gravity drained it back out.
Water came in to #1 which was connected to #2 via huge bulkheads at the bottom of the sides of both tubs. Then I had a bulkhead on the bottom of the side of tub #2 and pvc coming up and over the edge of my smaller tub #3. Gravity pushed the water up and over and on pump failure #1 and #2 would level out to the height of the pvc.
FYI tub #4 was above the rest as a fuge...small pump pushed water up to it and gravity drained it back out.