That appears to be a vacuum hose. I'm not sure there is any "official" way to connect that to a backwash port. Most backwash hoses are the flat kind that roll up like a fire hose (Some people even use fire hoses). They slide over the backwash port and clamp on with a hose clamp.
Maybe someone will be able to suggest something but I haven't seen anything around about connecting one of those to anything but a vacuum port. I would worry that sliding it over something (Some type of reducer fitting) would result in it shooting back off once the pressure of the backwashing water hits it...
Hmmmmmmm let's see who's creative out there!