I turned off the water supply valve to my toilet (a push-pull type with the supply line crimped on) and disconnected the water supply line from the toilet (the other side does not come off apparently as it is crimped on to the valve).
After reattaching the supply line to the toilet and turning the water valve on again I am getting leaking on the line where it meets the toilet that I was not getting before all of this.
The supply line is crimped at the valve, and appears to be white rubber (at least on the outside) with a plastic nut to connect to the toilet.
If I move the supply line a bit when the water is on, the leak moves around and in some cases can spray out a lot, while other times it will just be a small spray or leak.
So far I have just been hand tightening the plastic nut and tightening it a bit at the end with a spanner, but it doesn't appear to be a problem with how tight it is (I could be wrong on that).
What can I do to prevent the leaks when I turn the water back on, aside from replacing the whole valve and supply line (which is not an option)?
Final update: Just to close this out, the issue was the washer. When the supply line was unscrewed from the toilet the old washer fell out or disappeared in some way, this caused water to jet out between the nut and the hose whenever the water was turned back on. I contacted the original manufacturer of the valve/line and they sent me new washers which have completely solved the issue with water leaking.