Added my vote also.
I just want to expand a bit on the "no emergency drain" concept to see if the below makes sense to anyone:
As I noted earlier, if one designed the sump properly, and have a properly screened drain intake, the only concern you may have with this method (minus the emergency drain) will be the prospect of your return pump running dry due to slow clogging, therefore cause demage to the pump and the livestock.
When I experimented with my system by not making any adjustment, waiting for the slight clogging to do its damage, I never let it reach the point of the return pump running dry, but it usually took a week for the water to drop very low in the pump chamber to be close to the pump intake. Which means I would have enough time to correct any clogging problem.
Now what if I let the water continue to drop so the pump start to suck air? How soon should we expect the pump to run dry, get demaged, or to see livestock in the tank dropping like flies?
Well not anytime soon, certainly will be much longer than a week, because once the pump starts to suck in air, the flow rate drops, and so the system self-adjust to balance out the slower flow rate in the drain (due to minor clogging). We all know that pumps sucking some air will do no harm since skimmers use pumps to inject air all the time, and as long as there is water pumped through at the same time.
What you will notice is air bubbles begin to show up in the display tank from the return nozzle. So the question is really how long does it take for a reefer to do something about it when he starts to notice the air in the main tank, assume he totally missed the water level change in the sump for the last week.
Or the question should really be, if he still manages to allow the pump to run dry after all this time, is he really qualified to keep a reef tank in the first place?
Of course if an auto top-off is used in the sump this will not work.
