I used some tap washers, 7 in total, mine were slightly too big and had no holes in the middle, ideally you'd want to find some with atleast holes in about 5mm to take a m6 threaded bar or like ive done a 5" long m6 coach bolt.. my washers were also too wide but i just stuck them on the bolt, put it all in the cordless drill and sanded them down with 80 grit till it brought it down to the ID of the 22mm pipe, about 20mm..
stuck the long nut on for tightening and the smaller ones just to hold it still, ive used a hole punch on the two end nuts to stop them moving after tightening them both together..
steel washers are 15mm OD and 6mm ID though ive used two different sizes upto the rubber washers im going to make another one with the right size steel washers.. i got all the bits from a local diy store and the pipe sleeve from B&Q which is 8 OD & 6 ID but its aluminum and i think it might be starting to flair as its all tightened up so might change it for some steel tube..
those jet swets are good for 5 bar apparently and mine holds back mains but im not even sure what sort of pressure i have, i only plan on capping the F&E for the power flush because im cheap and not willing to stick a valve on the 22..