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Discussion Starter · #1 ·
I had an idea, then saw that others have done this too. I use canisters, not sumps but my tanks are big enough to rattle the nerves when thinking about a leak.

I turn the canister off during water changes because the spray bars are a bit much to deal with when they are a foot above the water level and I'm usually trimming, vaccuming or something in there at the time.

Is there any downside to drilling a hole into the intake at a point that would be a couple inches beow the water line? And if there is no downside, what size bit is recommended? It would need to be big enough to break siphon but it is an unfiltered hole that is sucking in water so you wouln't want it to be too big. (I use prefilters on the intake) I would think the hole size need would be dependant on the intake tube size and I have a 3/4" ID intake on one tanke and a 1" on the other.

PS - for those who don't know, this hole would prevent the water below the hole from siphoning out of the tank if a hose cracked or fell off...or if a seal on the quick disconnects or canister began leaking. 120g of water on the floor = :eek5:
 

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I've never drilled a tank, so bear that in mind when you read my opinion:

I'd drill as if I was doing it for a sump. I think it's the better part of wisdom for future planning. If you drill in a bad place for a sump, you may eventually kick yourself for your choice. You can always pipe in a few extra bends/etc to get the spray bar/intake where you want it for the canister filter. (You might be able to do the same for a sump... again I've never done/had one myself.)

As far as the hole goes: I'd try experimentation. The longer your drop and larger the pipe diameter, the bigger the hole will have to be to manage to break the siphon, like you said. You can always make a hole bigger.... I'd start with a small hole, set up the system, and let it drain into a bucket to see if the siphon breaks. If not, drill the hole out a bit bigger and repeat. Eventually you will find your own answer. Be careful about keeping up with the water changes so you don't kill your filter sucking air.
 

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There's always a chance that you could have a catastrophic failure but with canisters it's more likely problems will start out as a very small leak that should be easily seen (if you look). Just as likely your tank could blow a seam IMO.
 

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if you try it.. there are things to consider..

one.. glass
what kind of glass do you have.. drilling tempered glass is just next to impossible (and maybe just that unless you have special tools). If you have a plate glass.. then drilling can be an option.

once you drill it,, what fitting do you plan on using? if you have a pvc hole thingy.. (I don't know what they're called), then I would actually err on the larger side because the flexural stress caused by it on the glass would be less than a small hole connection. if you stress a small connection too much, something will have to give.. and glass has a tendency to do that sometimes.

pick your drill bit according to your fitting size (ie find the fittings you wand to use first). I would suggest a filter on the intake rather than actually trying to size the hole to 'filter' it. After you know the fittings you plan on using.. size the hole accordingly. (make sure you get a diamond bit instead of a carbide bit.. they will last multiple drills, never know when you'll want to drill another hole)

go slow.. drill slow.. you don't want to have to start over.. .. and to tell you the truth .. I'd never do this on an established or set up tank.. a dry tank that hasn't been set up.. sure.. but not a set up tank.. if you get one crack from drilling (not hard to do) then you can't chase it down. .. well you might but it'll always be a problem


I suggest sticking with what you got,, use a skimmer intake if you're worried about water on the floor upon failure... if you think you're brave enough, get some plate glass to practice on first.. plan the fittings.. then spend a day meditating before starting.

here's a good link on the 'how'
http://www.wikihow.com/Drill-Holes-Through-Glass
 

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Is there any downside to drilling a hole into the intake at a point that would be a couple inches beow the water line? And if there is no downside, what size bit is recommended? It would need to be big enough to break siphon but it is an unfiltered hole that is sucking in water so you wouln't want it to be too big. (I use prefilters on the intake) I would think the hole size need would be dependant on the intake tube size and I have a 3/4" ID intake on one tanke and a 1" on the other.
from what I read, he is interested in drilling the tank.. I don't know how drilling an 'intake' on a canister filter a few inches below the water line (top?) would save anything from not siphoning. Eheim filters have an intake at the bottom but if it fails.. the siphon will still pull water from the tank.. not the filter.
 

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The output in this case is a spray bar at the top of the tank. If the output hose came off the canister the tank would drain down to that point. The intake is more towards the bottom. If the intake hose fell off the canister the tank would drain down to the point where the intake reaches. With the right size hole drilled in the intake towards the top of the tank but under water normally if the same thing happened with the hose the siphon would break when it reached the hole he drilled. That is if the algae or a leaf didn't plug it up. lol

I've done the same thing with SW systems where there were multiple tanks using a common sump that wouldn't hold all the back flow in a power outage. That was on the return lines and it took some experimenting to find the right size to break the siphon.
 

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well that makes way more sense... :)

as far as THAT goes..
.. almost any hole you felt comfortable with (maybe multiple little holes) would work .. though the effectiveness would vary.. as the water is pulled in the siphon up the intake,, the negative pressure is greater as the water drops.. rendering any hole you drilled more and more effective

for a 3/4 inch and 1 inch pipe I would think a few 3/32" - 1/8" holes would suffice.. the water would mostly come from your filtered intakes.. debris may clog them but it would be almost no work to keep them clear (especially if you had multiple holes. 3-4 holes would definately allow enough air to get pulled in after the water dropped an inch or two below them to break the siphon)... you could test it on some extra bits outside if you had something.. buckets .. ladders.. I can see it now.
 

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I would put some floss or filter media in the whole so unwanted animals don't end up in the filter. Especially if you are already using a pre-filter.
 

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Discussion Starter · #11 ·
Gotta love when a topic catches up to what is in my brain on it's own! LOL

Yes, hole in the tube... Not the glass. I thought about the test method and increasing hole sizes as needed. Also thought about wrapping a woman's stocking around the tube to prefilter. Honestly, that kinda thing's not my bag baby! :red_mouth

I tend to agree that this may be overkill but I'm also wondering... Why not?
 

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You can drill the intake, but on a canister, there is not a big advantage. On a sump, the return can back siphon, so a hole is drilled, as you suggest, to prevent this occurring during a power outage. With a canister, it is a sealed system, so there is nothing to back siphon unless you have a major failure.

I've had floods from sump back siphoning many times. I don't ever thing I've had that from a canister, although may things are possible.

The bottom line is that you could do it. It's not going to hurt anything. If your going to do it, I'd drill the intake and the return. You do need to keep the holes clean. If they clog, they will not work.
 

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You can drill the intake, but on a canister, there is not a big advantage. On a sump, the return can back siphon, so a hole is drilled, as you suggest, to prevent this occurring during a power outage. With a canister, it is a sealed system, so there is nothing to back siphon unless you have a major failure.

I've had floods from sump back siphoning many times. I don't ever thing I've had that from a canister, although may things are possible.

The bottom line is that you could do it. It's not going to hurt anything. If your going to do it, I'd drill the intake and the return. You do need to keep the holes clean. If they clog, they will not work.
I think the issue is that the OP is preparing for the hypothetical failure where the pump house leaks, or the hose falls off. Not likely.... but don't think the hole will hurt anythign.
 
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