Fixed Tailwater Condition in XPSWMM

I have only been using XPSWMM for about 2-3 months on and off. Our client is repeatedly asking to have our outfalls as a fixed tailwater condition / make the tailwater elevation the top of the pipe. I have looked all over the internet for hours and spoken to innovyze support multiple times with no luck getting more information. So, I am wondering if there is any way I can produce a fixed tailwater condition for the outflows into the ditch/natural conduits. If there is no way to do a fixed tailwater condition, can I make the tailwater elevation at the top of the pipe?