On a recirc. system you want the dip tube 'all the way' to the bottom 1. to 'chop-up' and emulsify the water by pump action. 2. to get down where all the 'nasties' settle out by gravity.

On a recirc. system you 'can' apply a 'water absorbing' filter ... one loaded with a 'starch' similar to that found in 'absorbent baby diapers' OR use a 'water shedding' filter, etc. to separate the water into the bottom of the 'bowl' of the recirc. filter housing, etc.