I've made my own kitfro my brakes single axle Rapide
Standard hose into the hub flush port each side - warmed the hose in boiling water to make it malliable to fit inside the port before cooling. Cable-tied hose to along trailer to front on each side. Connected to Hozelock T piece,
Now connect hose T fitting to flush both hubs at same time whilst doing other post trip jobs.
Flush engine separately.
Simples and cost 10 quid or less
LT