How to stop Sump Drain Gurgle?

[fkshiu]

If you've got an overflow with 2 bottom drains (e.g. AGA Megaflow), there's the "Herbie" method from RC. It's essentially 2 vertical standpipes in the overflow, one taller than the other. The shorter standpipe flows down into the sump through a gate valve which is adjusted so that the overflow water level is at a height between the shorter and taller standpipes. Don't have the link with me now, but by all accounts it's dead silent.

If that's not possible, I've seen people put a Stockman standpipe on the final downward elbow before the water hits the sump.

The gurgling/splashing is caused by the air that's introduced from the overflow. A Durso, while silencing the overflow, can actually make the gurgling at the sump worse because of the additional air it introduces up top.

The Herbie method is silent because there is no air introduced in the first place. Water merely falls down by gravity. The Stockman just before the sump method works because the air added up top gets flushed out by the Stockman just prior to hitting the sump.