Confusing observation while installing bidet

[plumb_user]

Hi there,

I was installing a bidet and in the process, made an observation that I wanted to clarify.

I had shut off the main water supply to the house, so did not think about turning off the shut-off valve right besides the toilet.

When I detached the water supply hose from the base of the toilet tank, besides the miniscule amount of some "left-over" water in the hose, I did not observe any other water coming out from the hose. I presumed this was the case since I had turned off the main water supply.

Now, before connecting the hose to the bottom of the T-valve, I was trying to insert a washer in the hose to get proper seal. In this rudimentary process, I am not sure what happened (whether I touched "something" in the hose connector (the "white screw" that is tightened)), suddenly water started coming from the hose at a decent rate. Is there any possible explanation for this ?

I then tried using the shut-off valve right besides the toilet, and bingo, that stopped the water.

Appreciate any inputs here as this is quite hard for me to grasp.

Thanks a lot.

 

[MicEd69]

When you shut of the main water valve, that simply keeps water from coming into the house. But the pipes in the entire house are still full. So, any water in pipes that are above the point where you open the system is free to flow out of that open connection. But for it to flow, it needs air to enter the system as at that point it is a closed system. Since you only opened a 3/8-inch line, it appears that the surface tension of the water wasn't allowing any air to enter the system, just a guess. So, when you tried to insert the washer, you broke the surface tension allowing air to enter and the water in the pipes above that point to flow out. or someone could have opened a faucet anywhere in the system and provide the air for the piping to drain.

 

[Twowaxhack]

water heater probably started to siphon some.

 

[plumb_user]

Thank you very much for your kind replies.