Dad the grey pipe on the left is linked to the washing machine, it got loose and leaked. How do I stop it happening again?
(reddthat.com)
I think all the other comments are making it too complicated.
Completely unscrew the collar where the hose meets the pipe.
Position the hose so that about 1" / 2.5 cm is inside the pipe.
Screw the collar back on. The pipe should tighten onto the hose. Give it a tug to make sure it's secure.