Hoses become clogged inside with Lime scale and a periodic slow flushing with extra strong vinegar 12% will help to dissolve the lime and keep the toilet hoses clean.
Fill the toilet bowl with vinegar, 1 very short flush, after 2 hrs another very short flush until all the vinegars gone from the bowl. Don't flush with fresh water until the next usage as the longer the vinegar stays in the pipe the more successful will be the cleaning.
When feeding new hose through lightly coat the exterior with washing up liquid, it'll help the installation, wipe of any accessible excess after fitting.