I have a gravity fed system with port and starboard tanks draing to a mutual "T" then to the racor filter. On each tank top is an inspection port that has a dip stick, return ,,pickup tube,,on/off and vent,, ball valves.. i can unbolt the inspection port and the pick up tube will go down to the bottom of the tank...... last year I had the tanks scrubbed and clean as much as possible (there are 2 baffles in the tank). However in the pickup tube there are screens that were clogged.........I thought we wemoved them but quite honestly I cant remember. My point is....last weekend I was getting ready to go out and noticed that the Starboard tank was almost empty....all valves are open,,, so BOTH tanks should drain at the same speed...correct??? So Im thinking ... A). the pickup is clogged.on the port tank.. B). the vent is clogged on the port tank. I will check this weekend....BUT...if I pull the pickup out of the full tank...... Will I introduce Air into the system?????,...causing me to bleed the injectors????...not a fun project....or if I shut the tank OFF with the ball vales will this stop the intake of air? Thoughts??? Thanks Rob