overflow to sump ?

[darb2]

When plumbing an overflow, should the outlet of the drain be above water, or below?

 

[RMPD109]

The outlet off the overflow box should be submerged under water in the sump. If it is not you will get a loud trickling/waterfall noise. The outflow pipe in the overflow box will determine the water level in the overflow box. It should be at a height that allows both ends of the U tube to always stay submerged (to keep siphon).