Interestingly the recent late season rain has the Deep Tunnel almost full. [1] Two of the three main reservoirs are already at capacity, and the the last one is getting there.

BTW they do offer tours of the pumping stations, but not the tunnels [2]

[1] https://chicago.cbslocal.com/2019/05/01/heavy-rain-flooding-... [2] https://www.mwrd.org/irj/portal/anonymous/tourinf