Need more sump capacity for backflow... how? Dual sump/fuge tanks?

[hocky]

2 29's is probably a good option. A HOB overflow would be an easy way to get it up and running quickly, but if the tanks are approximately the same height, will there be enough gravity to maintain a solid syphon?

 

[wattsupdoc]

As long as there is a difference in the water level in the 2 tanks you'll get syphon with a HOB OF. The lower the water level in the one being fed with it the greater the flow can be. To a point anyways. However, you could just drill the 2 with a couple bulkheads and be done. It'd be a lot cheaper than a HOB OF. Less maintenance, less worries.
If you do the HOB, then I'd do the skimmer and return pump in one, the other all fuge. If they are both level with each other, then the backwash will be able to be accommodated in both tanks. If you actually have 20 gal. of BW, then just the space remaining in 1 , 29 wont be sufficient. Here ya go.
HI TIM!

 

[987654321]

If you have 15 to 20 gal of back flow I would suggest fixing that first. The twin setup is cool and if you have the room def go for it. But I would def cut down the back flow. Thats just more water you can have in your system. I have a 125 tank and maybe have like 5 gallons of backflow with the pump shut off.
I didnt read through all of the posts here so if this was already mentioned im sorry.