I replaced the conduit runs routing preference to include a “thin” coupling. which is only 1/8” long so short conduit runs shouldnt really matter
if there happens to be a conduit run that is 1/8” long and it cant fit the coupling in there, then just skip that one it wont matter because we can separate by the fittigs at that point
allright try something here and see if its more stable…i send you my costum dyf, you just can place in your defination folder..the issue with conduit and cabletray is keep the connections, much better with ducts and pipes, but keep in mind i have only tried on your shared sample, on 6 runs, there could probably be other situations in your project…dont know 
but here is the princip..
forum_union.dyn (42.6 KB)
SOVI_union_insert.dyf (6.8 KB)
Good afternoon @sovitek it works pretty good on the original six! I tried it on a few more runs and only had a few pieces that revit wanted to delete, because it said it needed to, however as you can see here there should be plenty of length for it to have added the coupling. Do you know why it is deleting these? Please see attached
Project5.rvt (8.5 MB)
update… I got my main concept added to this script and got it working to a copy of your first python node when left in isolation from the rest of your script but when i tried to connect it to the rest of your script it failed more so than not connecting it. Meaning more conduits were deleted than your original script and also the connectivity of the conduits was a lot more broken. So ‘tab select’ only selected a few conduits and fittings instead of the entire run did in your last script. I suspect this might have something to do with your “wait” nodes but I thought I handled that properly too. please see my script below. Please advise.
as mention but its all about sort a list
Good morning @sovitek I dont understand what actions to take next. I mean I understand how to sort my lists. But Im not understanding what, if anything I can do to fix this. Please advise
