Is it advisable to use a garden hose with water ON ???

You can do, but consider that a blockage can be made worse by the
addition of a spray nozzle off the end of a hose ;-)

I was thinking of the hose with no implement at the end.
Anyway, removed toilet, and blockage was in T-junction outside (upstairs).
Cleared by pushing a piece of garden hose (no water) through the bends, and
then rotating it to clear "substance" that had over the years narrowed the
pipe to the extent that toiletpaper couldn't get through. Alternated this
with pouring water in. Lovely smell, family fled.
Works fine now.