Returns are lower than overflow - how to prevent flooding sump?

[somekindabonita]

I could use some help figuring out the plumbing on my tank. I bought it used so we didn't have to drill, but after some further research have realized the setup isn't the best. Trying to determine our best path forward from here- any suggestions are appreciated!

There's no overflow box, it's just two inlet pipes so it's pretty noisy. My bigger concern is the return nozzles are actually lower than the overflows.
I have them turned up to the surface as much as possible, but the nozzles still leak by slowly through the bulkhead and will overflow my sump when we lose power.
Drilling a hole at the top of the nozzles won't work since it's not actually a siphon causing the issue.
I have a check valve on order to install in the return line, but heard they're pretty likely to fail.
Our stand doesn't have enough space for a larger sump, and we can't run the current sump at a low enough volume to hold the overflow of water. Also can't replace the sump with a different design as you have to drop the sump in from the top (meaning removing the DT totally).
Have a small generator, but want a fail safe for when we're not home. We're also renting, so an automatic generator system isn't an option.
Seems like the battery backups won't run the return pump for very long at all.

What do you think is our best option? Just finished our cycle and added the first fish this week, so would like to try and fix this before we get too many more inhabitants!

 

[lapin]

There's no overflow box, it's just two inlet pipes so it's pretty noisy. My bigger concern is the return nozzles are actually lower than the overflows.
I have them turned up to the surface as much as possible, but the nozzles still leak by slowly through the bulkhead and will overflow my sump when we lose power.

If your nozzles leak then you prob need to replace them. If its just a higher posistion thats needed to prevent a leak back...... It looks like loc-line. You should be able to get pieces that are longer that you can exit higher than the originals.

 

[somekindabonita]

The joints in the return nozzles aren't supposed to leak? We had figured slow leak by was normal for that type of connection between the bends. Will definitely look into replacing - that just might be our answer!