I usually make 100 ml batches and it takes about 2 hours to filter with a .22 whatman. My hands and fingers are very sore by the end. you would have to bee really tough to filter 400ml at once through syringe filters. You can place the syringe in a vice so that you don't have to hold the syringe in your hands and the just press the plunger, makes things a little easier.