[Madmak]

There is also quite a difference in start up noise and duration between the Herbie and Bean Animal. A Bean Animal typically balances itself and purges all the air out in under a minute, Herbies generally take a bit longer. This is always a noisy process.

A full siphon drain carries the maximum amount of water possible. With the downturned elbow up top in the overflow everything is silent. Open pipes are not silent. The secondary drain is essentially an open pipe due to the vent. You tune the main siphon to take 99% of the return pump's water, from the down turned elbow to the submerged bottom exit. This lets 1% of the water down the secondary which is near silent as the only place for noise to escape is through the vent. When a blockage occurs in the main siphon the water level in the overflow rises. When it reaches and submerges the vent line it turns the secondary in to a full siphon and quickly drains the overflow. Very safe backup system. The third pipe is just an emergency drain meant to stay above the maximum overflow water line and dry at all times. It is only used if there is a blockage is both the primary and secondary drains.

The sanitary Ts are not required, normal Ts work just fine. Your tank is drilled through the bottom do no Ts are needed for Herbie or Bean Animal styles. The Ts in a Bean Animal are also there to provide access to clean the pipes occasionally. Herbie style drains are quiet and safe, Bean Animal Style drains are quieter and safer.

IMO a Bean Animal style drain on an external coast to coast overflow can't be beat for performance, safety, or noise level.