I use a 5l measure jug like mechanics use & just cut the nozzle open to let the balls flow freely. They will hold a couple of bags but I just use one at a time for ease, cost around £8.50 each (I just happen to sell them so mine was a bit cheaper!!!!!!!!!!!) usually available from any good motor factors like Wilco / Halfords etcPut all your paint in a empty box and scoop it into your pots.
One good idea I seen down at the masters was what looked like a old plastic watering can with nozzle cut right down, seemed to work a treat.
Andy/Fredo
LOKI