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.
Note that the "Event type" is only there for inclusion in print-outs - it doesn't calculate the different AEP discharges.