We have very hard h20 where I live so once in the past, when my flusher became difficult to push down, I replaced the red valve seal (like a giant rubber washer) which corrected the problem (I was told that when the seal wears out, it acts as a suction and can eventually break the flusher.)

This happened recently so again, I replaced the red valve seal. Unfortunately, this time, water from the tank was seeping back into the bowl so I was told to replace the entire flush valve, which means removing the tank from the bowl. After some trials and tribulations, I was able to do that and reseat the tank on the bowl.

After reattaching the tank, I tested the seal of the 3 bolts (that anchor the tank to the bowl) with water from a glass and none of them appear to be leaking. Then I set out to reconnect the rigid water line to the tank. Apparently I should have just uncoupled the nut from the top - it's code in the city to have a rigid water line - because when I put the line back together water is coming out of the top where the coupling nut is. I've tried tightening it, and loosening it. There's a little yellow washer-like piece that sits into the top of the rigid metal pipe on the south end but it just rests flat against the plastic tubing and then the coupling nut screws over the top. (see photos)

I really can't replace the rigid line with a flexible line or it will be a problem when we sell our condo. Are there any other suggestions or options that anyone can offer?
Many thanks!!

The upper flat washer is either not sitting square on the fill valve threaded pipe or the washer is damaged and needs to be replaced. However, I suggest you still try to install it again - this time starting from the upper connection. Remove entire line, attach upper connection , then bottom connection. See if that helped. Back to you / Milo

Milo - Thank you so much for taking time to respond. I'm really determined to make this work but with the number of trips to Home Depot and my Mansfield supply shop I'm losing steam. ;)
I have removed the entire line but it's such a tight fit that if I attach the top without having the bottom sitting into the pipe (you can't really see that part in my pic,) I can't get the bottom part connected... The bottom part of the rigid line has a little curved piece on it that sits into the water supply pipe. Does that make sense?
I'll go try one more time (I've actually already tried 3x to get it lined up just right) and them maybe I take the whole thing to Home Depot to replace the yellow washer?
Just a note, my toilet/supply line etc. are in a condo built in '06/07 so not that old.

..

Well I wish I could say I made it work with the fixed supply line but I just couldn't get it to line up correctly. HKStroud, thank you for your detailed drawings and response. It was the original line so the length (in theory) should have been correct. I replaced the washer, even though the original didn't seem to be compromised. Wish I could have someone come out and make it work but really don't want to spend the money on it. Finally I gave in and purchased a short flexible hose. It seems to be working but I'll be keeping my eye on it and repost if this doesn't work either.
Thank you again to all who answered!
L