When creating your cross-section, you have the option of entering discharge information as shown below. If there is a low flow pipe beneath your cross-section you can select from standard pipe sizes from 100mm to 3000mm for Class 2, 3 and 4 pipes. For other sizes, a Non-standard pipe option is also provided. Of course there is a "No pipe" option.
The Pipe Flow Calculator can also be useful for estimating the flow in pipes when you know the grade of the HGL.
Note that the "Event type" is only there for inclusion in print-outs - it doesn't calculate the different AEP discharges.