mordgrow, I'm not plumbing in water to my grow closet. I am using that filter to filter my nutrients while I use my pump. I wish I had a drain.
ocitown, it's possible to do a circulating DWC system with a reservoir. It will add more hoses and stuff to your system. I plan on keeping mine simple (less to go wrong). I am cool doing it manually every day while I visit my girls. My friend mordgrow is building a circulating DWC system to a plan at this site
http://www.icmag.com/ic/showthread.php?t=26343.
I don't give all the details of DWC growing in this thread. This is more of a DIY system build. I will tell folks how I grow my weed if they ask, but I suggest you take my growing advice with a grain of salt. I don't consider myself as an expert in hydroponics. Lots of the stuff I do is copied from a grow instruction for dummies.
I flush with water the last ten days before harvest. I don't add any thing to my water.
Peace, R.