This is in relation to using or not using T fittings coming out of the back of the bulkhead.
The sketchup I have seen shows T fittings, but I have also seen elbows coming out the bulkhead down to the sump.
T-fitting
Elbow fitting
Other than the obvious answer (1 uses a "T" and the other uses an elbow) what is the difference / benefit of using one over the other?