Overflow question

[mitremark]

When setting up a tank with 2 overflows is it okay to have the 2 drain lines meet at a "T" and then drain into the sump or should each drain line empty into the sump by itself?

 

[scsinet]

The two can meet, but remember that overflow lines need to be free flowing, so they need to terminate into a larger pipe, preferably one that's 300% larger than the two overflow's pipes.
One of my tanks has dual overflows, each with a 1" bulkhead. They drain into a 2" pipe. A 2" pipe is over 3 times the size of a 1", because the size of a pipe's effective water carrying capacity is the area of a circle. The area of a 1" circle/pipe is .78 square inches, 2" is 3.14 square inches.

 

[mitremark]

If I understand correctly because I'm using 1 1/4" hose that would mean i would need at least a 2" "T" so that the hose will be big enough to drain freely.

 

[scsinet]

Yeah I'd say 2" will be okay. You're spot on, the big key is to have the pipe be big enough that water easily flows, with no restriction or holdup.