I've just been looking at this again now. Looking at my tuning I did remove the flush coding because it meant that Sims would reach through the wall which I obviously did not want.
I attempted to add the code you have quoted here, @Triplis , to the Pee tuning instead, attempting to skip the middle stage of flushing first but it had no affect. Sims still pee, finish, and then just stand there. I may not have ccpied it exactly though or into the correct area so I'll take another look and see if anything I do makes any difference.
Thank you for the feedback the both of you. It is much appreciated.
ETA: It works! I had stupidly overlooked a single line. Instead of True I had something which forced the Sims to use the same object for the follow-up action. Seeing as washing hands on a toilet isn't possible, that's why it was failing.
ETA2: I've now successfully got the game to check if they are slobs or have bad manners and if so, they will not wash their hands. I was worried it would disable being abel to use the urinal all together for those Sims but thankfully that was not the case.