As long as the skimmer keeps the waste up in the top of the tube, then adjust for a dryer foam to get the dark green/black gunk. On the other side of the coin you do not want clear or weak tea color too much water, so find a place somewhere inbetween that suits your system. the euroreef Im running does not have a cup drain and pulls about 1/2 inch per week of very dry foam, however, once dumped it takes straight bleach to cut the smell and it has to set in the drain for at least 20 minutes. really foul and very strong. so both biff and hawk are correct. you will need to choose your point that seems to do the best job. good luck. keep us posted.