Check the bowl the strainer sits in. I had a similar problem with mine. Couldn't get pressure with any sink valve open and took a long time charging to pressure. The bowl turned out to be cracked and it was sucking air into the lines instead of water from the tank. I took the strainer out a couple times thinking I had sediment clogging it up. I sometimes fill from a creek while dry camping for extended periods. Finally noticed the crack at the bottom of the bowl while wiping it out. Glued it back together with some JB Weld and not had another problem. Just got to remember to take the bowl off while winterizing. i figure the crack was from water freezing.