Star systems optima 1202 power flush toilet

[TRiddley]

This seems to have a stoppage or drain problem. There is a shower attached nearby using same water line. Water backs up in shower when in use. Water leaks from power flush unit. Plumbers I had come didn’t seemed knowledgeable of setup and I’m paying but no fix. We figured defective unit. Installed new one , shortly thereafter, same problem. Any suggestions?

 

[Fitter30]

Where's the leak on the power flush unit? Showers water line are writing about the drain line? Look at page 18 diagram 3 check valve or the drain line is partially stopped up.
www.manualslib.com/manual/2069960/Star-Powerflush-Optima-S1201.html?page=1#manual