about 20 years ago me and a buddy who worked for us,invented a pneumatic grouter.it held about 5 gallons of mud,had a spout at the bottom for a grout hose,and chuck for air at the top.we used an old inner tube for a gasket,and wingnuts to tighten the lid down.it worked good for about 5 mins.the air pressure slowly pushed the grout out into the hose,but it would soon go down the side of the tank and find the hose.hell we had visions of making millions on this selling them to golblatt!
anyway,until someone comes up with a better way,the grout bag is the only way to go.and the best way is lay about 20 sqft and grout.that way you are not wearing your hand out.i do not twist the bag.i hold it in my hands,use my left hand to guide the bag and squeeze with my right.fill it about 3/4 full and squeeze out a small amount to get out any air pockets.