To avoid all kinds of explanation questions; let me set the stage for this question.
Zinger, ZT25SB, winterized, water heater bypassed and empty, tanks drained via low point drains.
Now, as I've done for years with my motorhome, I prepare a bucket of bleachy water, put the suction hose in the bucket for the pump, start up the pump and try to pump chlorine water thru all the piping, out the outside shower into my water hoses (those I use to supply water to camper when camping) so I can dis-infect all hoses and piping. Turn on the pump and I get water out of each faucet, red antifreeze first; then clear water but it has a lot of air in it. pressure is low. Keep pumping water til all lines are clear of antifreeze. But, lo and behold, the water in the bucket has not gone down! Oops, I forgot the valve to connect the suction hose to the pump. Turn this valve on and now the bucket starts to empty and I chlorinate all lines as described. So, question is, where in hell did the water come from when the bucket was not connected? Was there residual water in the fresh water tank that didn't drain out when the drain was opened? Mystery Mystery Mystery.