My first tank ran an eshopps overflow box with dual drains and was a PITA when lost siphon. Not sure about nowadays
There was a defect if it lost siphon – ait has to be able to get into the siphon tube. Guessing, it was probably a hairline crack in the siphon tube. Same here, returned it. Ended up with a different overflow altogether since that was the last Eshopps they had.
They are noisy out of the box but can be fixed with a diy Stockman Standpipe for a few bucks.
I'm with you all in that I really like mine...
Usually the noise is from too much flow.
You'll get 50% of the drain's rating in silence, but above that there's gonna be some noise of some kind, so you have to size accordingly.
Adding something like a maggie muffler or stockman can help, but only to a degree –
glad it's working on yours! – but it is easier in most cases just to dial back the flow a little bit until the drain gets quiet.
I lowered flow and removed the mufflers on mine. Since then, it's been about 10 years of never having to fiddle with the drains over noise.
Expect that final flow rate to be about 50% of the drain's rating, as mentioned. That's about 300 GPH per siphon tube. Ideally one tube per 75 gallons of display, two per 150 gallons – but you could support tanks double that size, depending on exact requirements.