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Okay, I just picked up a new (new to me anyway) tank which came with a pump as well. The tank is an 85 Gal. and has an internal corner overflow. The pump is a Mag 18 submersible rated at 1800 GPH. At 3 ft. Head it looks like it will be around 1500 GPH.


The first question is related to all of the holes in the overflow. In the bottom it has one large hole that will fit a 1" bulkhead fitting. It then has 2 other holes that fit 1/2" bulkhead fittings however I can make DIY bulkhead fittings that are 3/4" to fit them. In the side of the overflow (the side closest to the back wall) it has 2 holes that are the same size. These are at about 1" and at about 6" below the water line and overflow baffles? (Slots or whatever the term should be) There is also a sixth hole (sort of) in the front side of the overflow at the top through the baffles. This looks like it will fit a 3/4" or 1" diameter pipe. The question is what is the intended purpose of each of the holes.


My initial guesses:

1" in bottom: Drain Line using a standpipe.

The other 2 smaller holes in the bottom: 2 return lines.

The hole through the baffles: A return line.

The 2 holes below water level: Return lines?


Obviously this doesn't add up. There seem to be 3 return lines in the overflow yet only 2 through the bottom.


Alternative guess:

1" in bottom: Sump drain Line using a standpipe.

The hole through the baffles: Sump return line.

The other 2 smaller holes in the bottom: A closed loop system.

The 2 holes below water level: A closed loop system.


This results in each hole having a purpose.


The next question regards how I should set it up. While I could run 2 pumps (1 sump and 1 cls) I really would prefer to just use one pump I think to save on electricity. How much benefit would the cls be as opposed to just using a sump pump? My plan was to build a manifold with either 4 or 6 outlets for the return and then use 2 - 1" drains. (I would need to make one of the holes bigger for this) The issue there though is that each one will drain 600 GPH so I don't think it will keep up with the pump. (1500 GPH estimate) Even if I figure in some losses I still think I will be over 1200 GPH. This would mean going to a 1 1/2" drain and the associated costs for the plumbing whereas I already have everything for the 1" drains. So should I bite the bullet and add another pump to the power bill or should I spend the money for the larger drain and just use one pump and a manifold setup? Or should I do something different? And why should I choose one over the other?


If I do go with a CLS then what are the optimal positions for the returns?



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Some pictures


Here are some pics to go with the above post.


Here is full shot of the tank. The only thing I can find wrong with it is a small crack in the upper left corner on the front. (If you look close you can see it) I was told it still held water there however I went ahead and used Weld-On 4 on it anyway just to be sure.



This is a shot from underneath the overflow showing the 3 holes there. Thinking about it a bit more I'm still short one hole here even if this was set up with a closed loop system.



This shows the 2 holes on the side of the overflow. They are a little fuzzy but it should give an idea of the position. I'm still trying to figure out if these were intended for a closed loop system or for something else.



Here is the hole through the baffles at the front of the overflow.



At this point I'm leaning toward the closed loop system however I need to know if I should add any other returns if I do. I would rather punch any new holes I need to now than get it set up and then wish I had done so afterwards.





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My opinion:

I would run the large whole as a supply and tee it off out the wholes in the overflow. Then use the two small holes for drains back to your sump. I like having mulitple drains so you don't have to worry so much if one was to plug up. Also you can take one of the drain lines and use it to supply your chiller or skimmer. Just my 2 cents. Good luck, Mike

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Looks to me like whoever drilled it was hell bent on being able to put it flush against the wall. One large hole for the overflow to the sump. the two smaller for return lines. What I would do is run one return pump and use a Y to send the water through each hole to give more even flow. That was probably the original design anyway. I'm thinking the notches that are knocked out may only be that way to let a little more water flow in. Maybe it wasn't going in fast enough. I say this because the water stain on it looks to be pretty high.


Just another note: I would make sure you look into the gurgle buster for the pipe to the sump. I made one for mine and it made a world of difference. There is a recent thread I posted the link but you could google it also.


Here I grabbed the link for you. very easy to do can be had for about $5 at HD or lowes.



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Use the bigger one for a drain and use the Herby style. One small hole will be for an emergency drain and the other for the return. This will be dead silent and they work great. I have done both set ups and would not go back the the Durso style again just my opinion.

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The problem is that there is no way either the 2 smaller holes or even the larger one will drain 1500 GPH. The overflow doesn't have enough area either to drain it that fast. (Which could be why the hole is through the baffles)


Regarding the overflow I'll probably be using the Herbie method (I posted a link to it in that same thread) instead. (I'm already using it and the drain is completely silent) I looked at the Gurgle buster and from what I can tell it accomplishes the same thing except that it is done by limiting the flow at the end using extra parts instead of using a regular valve. Since I will already have a valve anyway there isn't a need to have the extra parts.


In order to drain enough water using the larger pump I need to bump the drain size up to at least 1 1/2 inches (2 3/8" hole). Then if I add a backup to this I'll need to drill another 2 3/8" hole. If I run it with a closed loop I eliminate the need to go with larger plumbing and can then run multiple returns.


My current thought is to add one hole in the side of the overflow at the rear of the tank that is almost to the bottom of the tank. Then I can plumb it out to the front 2 lower corners and cover it up with sand. Then I can utilize the hole closest to the middle for a closed loop input and the one above it to add 1 or 2 returns in the tank at the back. Those 3 or 4 would be on the closed loop using the larger pump (About 1800 GPH). For the top I can utilize the hole through the baffles using the sump return (450 GPH or so) to add a couple of returns in the front at the top. This should eliminate the 2 powerheads (500 GPH or so between them) which I currently run in my 55 Gal to supplement the sump return and increase the flow by a considerable amount (more than double) in the larger tank. Note: I'll need to add one hole in the bottom as well but I'm going to need to anyway regardless and using the closed loop it can be a smaller hole.

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