how do i fix leaking flexible hose under sink which keeps unscrewing itself when i use the washing machine?

The threads are possibly worn, or maybe they were cross threaded when first installed. It would be in my opinion best to replace the 'appliance trap', this is the U bend which sits beneath the sink outlet waste and incoroporates the fitting you describe. If you don't want to go to this bother, then try wrapping P.T.F.E. tape around the maile thread, at least ten turns !, then refixing the p.v.c. spigot outlet, tightening with adjustible grips. Also look at the angle that the appliance hose is joinning the spigot. Loosen the jubilee clip. if fitted and rotate the appliance pipe untill it is not working agasinst the thread of the spigot connector. Regards, Adrian

You may have a poltergeist who can use a screw driver,think you should contact the local priest and have him perform an exorcist! If that fails call me and i will sort it for you

If you are talking abut the waste then the grey hose should attach to the waste, pyramid style plastic waste with a jubilee clip this will secure it in place.

Hi Use a jubilee clip which you can buy from any diy shop. Hope this helps Regards Steve

You can change the type of Washing Machine Waste by fitting a 40mm Compression Tee with a Washing Machine Stem fitted into the compression fitting and then put washing machine waste on fixed by a Jubilee Clip. The best way is to have a washing machine upstand fitted where the washing machine waste hose is placed inside it. Bill Pipe Dreams Plumbing Services Bournemouth