I’m currently using a hob eshopps pf-1000 siphon overflow and will be drilling my tank for an eshopps prodigy tomorrow. The reason is while siphon overflows can go months or even years without problems, I’ve been lucky enough to catch mine acting up several times. What i’ve found is most of them have a fatal flaw. It’s the u-tube. Pretty much all of these overflows come with a u-tube that’s too big. While they theoretically can support a lot of flow, that flow is massively slowed down once it leaves the tank and enters the rear chamber of the overflow. This creates three problems: The first is the overflow is at the mercy of the drain attached to the overflow box. If you want a quiet drain, you’re going to slow down flow OR raise the water level in the rear chamber, which places backpressure on the u-tube outlet, slowing flow. This creates a secondary problem of potentially overflowing the tank if your pump puts out too much flow, even if the overflow box is rated for it. Keep in mind, these boxes are rated with zero backpressure in mind. This means they’re rated minus a slightly clogged foam or a durso in the rear chamber. No one runs their overflows this way because it’s insanely loud. The last problem is bubble accumulation in the u-tube because of it’s size and the above problems. Water needs to travel through them at high velocity to blow any trapped air bubbles completely through the tube. This is nearly impossible to do without leaving a 1” drain in the overflow completely open due to the pressure differential generated by water waiting to go down that drain and water trying to enter the u-tube from inside the tank. If Eshopps had supplied a 3/4” tube instead of a 1”, it probably would flow just as much considering the drain is the bottleneck here, while simultaneously forcing that volume to go through a smaller passage, which would increase velocity through the u-tube and clear bubbles.
In a nutshell, you want to go drilled whenever possible.
