I take it you are new to CAPD ? Everyone is different some people take 20 mins others take 40 mins. The easiest way to see if its finished is to watch or hang the drain bag on scales and obviously if the amount is not going up then your drain is finished, others might get a pinching feeling or tugging in your stomach, that also tells you that you are pretty much empty. You should get back at least the amount you put in plus a bit more , so 600 isnt good. You could try draining in different positions , sat , lay down etc, but if you have only just started dialysis i would give your clinic a ring and tell them you only got 600 back on your drain.