Pioneer 19t4 TT water tank problem

Update: Plumbed new from the drain on the tank. 3/4" to a 3/4x1/2x3/4 tee then to a drain valve at the side of the trailer, (Very convenient). Ran the 1/2 off the tee up to just above the floor (sealing the bottom entry) and then 90 degree with hose barb and hose to strainer and pump. Works very well. I pluged the outlet at the top of the tank, I believe the tank is vented through the small hose next to the fill line. Wife and I did an overnighter with four granddaughters and had no problems with the water system. All seems well.