Why do I fear SUMPS :)?

If the sump is set up correctly you have nothing to worry about. When you set your sump up you get your "running" level and never fill more than that. When your pump shuts off water will back flow into the sump until the siphon is broke. When my pump shuts the water level in the sump is about 5" from the top of the sump once all the water has stopped draining back in. I would tell you do not need a check valve. That is a FALSE sence of security. It will eventually fail. All it will need is a small piece of sand, slime or whatever stuck in the seat and you will flood out.

 

Agreed. Snail clogs the overflow, only the return section gets pumped back to the DT. Just make sure the return section is small enough

 

Not quite for mine. This grate is an overflow to the back compartment, where the normal filtration equipment is on my RSM250 AIO tank. There's nothing bigger than this for critters to get through to the back (notice the 1/2 inch hermit up there), so if any critters do make it to the back, they're small enough where they can't clog the U Tube.

The overflow itself, as you can (or may be able to) see, has foam both in the top of the drain pipe and in the hole where the U Tube is:

Then there's tons of room in the sump (this was just hit with the ATO a couple hours ago, and it dumps over a full gallon in when it triggers):

 

OK, I feel like I'm getting a crash course on sumps now, but I would be lying if I said I wasn't a little confused. I know many different folks have many different methods of running a foolproof system and so there's lots of different variations. Hence, some have experienced issues with some variations while others haven't.

I do understand the "making sure your sump has enough extra capacity equal to the overflow so it won't flood in case of outages, etc".

What I'm confused about is what is drilled vs overflow?

 

An overflow is used in either case (an overflow is basically a baffle with teeth at the top).

The difference is that with a hang-on overflow, you have an intermediary; that's either a U tube, or a weir, out to another box external to the tank, and the water drains from there.

With a drilled tank, you don't have that intermediary water mover, so it's a simpler system, and less can go wrong (in theory). A U tube is very reliable, though, if you keep out any snails from the inner box and check it occasionally for bubble buildup. A weir isn't anywhere near as reliable, since it doesn't use simplicity to its advantage. They require a pump to keep out air bubbles (failure type #1: power failure means overflow failure), while a U tube, when set up properly, will have enough velocity through the tube to pull out its own bubbles, and won't break siphon on its own.

 

thx for the info BR.

my conundrum is best described in a picture:

 

Ahahaha. That why you gotta know how they work; knowledge helps alleviate fear.

 

wasn't it you that just mentioned about "the baffle with teeth", I'm a scared bunny

 

A properly designed sump is not a flood risk in any way shape or form. NEVER, EVER rely on check valves or drilled holes to stop a flood, the key is a correctly sized sump and proper placement of the returns and a flood is not a possibility.

Keep the returns close to the surface so you can easily calculate the total backflow before they break suction or create an air gap andalways maintain that amount of room in your sump and you can sleep soundly at night.
No maintenance or cleaning and no floods, an air gap is the only foolproof method of stopping backflow period.

 

Don't fear sumps. Sumps are awesome. Embrace them for the engineering wonder that they are. Oh, and don't screw the plumbing up or they will flood you house an ruin all your fancy shoes... I like my sump.