Originally Posted by Toffee
I was talking about return pump, where the water gets pump from sump back into DT. Its harder to pump water back up against the gravity and over long period of time the pump itself will wear out a little power and pipes if not clean will clog a bit.
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No, if you run a pump that is way over what the overflow can handle, considering headloss into the equation, that pump will empty the sump before the overflow is capable of doing its job properly. In other words, the tank will overflow.
But, you didn't mention this.
You can get a pump thats rated higher than the return is capable of handling, with this in mind. You need to T off the main return line to the DT, adding a ball or gate vavle on it, going back to the sump, this will allow you to fine tune the return to match the overflow.