Hey just a quick question, closing real soon here in michigan.. My 3rd year closing but I am confused on how blowing my main drain keeps water out of it? I never really thought about it, just followed instructions from the previous home owner, but anyways..
I use a shop vac and when bubbles come flying out of the drain I then close the valve and turn the vac off.
How does the water not go back down thru the drain a little?
I'm A bit tired and at work so my apologies if I'm not making sense.