Opinions needed:
Recently purchased a 300 gallon Planet aquarium. I had them drill 2- 1 3/4” drains and 2- 1 1/2” returns. I had planned on installing 2 Durso drains. My question is: Wouldni be better off installing 1 Herbie? Or would that not provide enough drain. Thanks in advance.
Without beating a dead horse, or trying to monopolize the responses you're getting, I'll give my bit after thinking about it.
With a 300g DT and a not yet known sump size ...
You're looking for about 255-280 Total Volume PLUS your sump volume.
The ideal amount of flow through a sump, as recommended by the web, is about 5.5x system volume. This number is derived from what many feel is the ideal flow for a skimmer. So, 280 x 5.5 = 1,540gph PLUS your sump.
You will be asking your drains to handle this flow. I recommend you plan your system so that ONE drain pipe can handle this flow.
Nothing worse than water on the floor.
You can play with this number as you feel, based on whatever skimmer you decide to purchase, and based on how many Total Gallons your system is, and the skimmer's flow requirements.
You posed the question about Durso vs Herbie.
Herbie is my recommendation - no question.
Now to your drilled sizes.
You had them drill, according to you, 2- 1 3/4” drains and 2- 1 1/2” returns
I don't know for sure what sizes your holes are, or what bulkhead sizes they translate to. I'm hoping it means 1-1/2" drains and 1" returns.
Regardless, If you run a Herbie with 1 main siphon and 1 emergency pipe, and 2 x return lines you'll be fine. But, I recommend you upsize the drains to 1-1/2" right below the box/right after the bulkheads.
I don't feel a single 1" drain will be safe enough. It can't handle the Gravity flow of a 1" pipe. Max is less than 1,000gph
It's up to you. I'm just trying to give you enough information to keep your floor dry.
You need to look at the total amount of water you'll be pushing with your return.
Think about this.
Your system needs to handle ALL the flow of your return pump in a situation where ANY of your pipes is THE ONE drain.
So, can your main drain handle the 1500+gph of your return pump in a No Siphon situation?
Or can the emergency?