I usually recommend that BM skimmers be setup in a small tub with 10%-20% warm vinegar solution and run the skimmer for about an hour in this vinegar bath to remove the production oils secreted by brand new acrylic. Use only white distilled vinegar, but warm tap water is fine to mix with vinegar. After an hour, rinse the skimmer in warm tap water and then install into your sump. Don’t worry about the tap water as there isn’t enough residue remaining on the skimmer to be of concerned.
Before you fire up the skimmer in the sump, check that the sump water level compared to the skimmer is between 6″ to 8″ deep. Fire it up and allow the initial foam level to settle down within a few minutes. Check where the top of the foaming level is and raise or lower the top of the foaming level so that it is just even with the bottom of the collection cup. The highest initial foam level should not be more than 1″ above the bottom of the collection cup. Leave it there for 3 full days. Even though you may be tempted to adjust the skimmer, just leave it at that setting for 72 hours. After 3 days, you will see that the foaming level has risen and this is a good time to see if the foaming level is too low. If it is, adjust the bubble breaking level up 1/2″ and wait another 24 hours. Next day, recheck the foaming level again and readjust if necessary, but no more than 1/2″ every 24 hours or you can overflow the skimmer. Some in sump skimmers are really sensitive, but if you take it slowly, you will get the desired skimming without overflowing the unit. Good luck and enjoy your new skimmer.