[C38] Vented loop for head discharge

[Steve Smolinske]

Question for anyone with a vented loop in their head discharge.   Looking at it on paper it seems that the pressure of the grey water in the section from the head to the vented loop would be enough to leak back into the toilet bowl.  I know there is a duckbill valve and a flapper valve in the head to stop the reverse flow, but as we all know if you leave the discharge seacock open the head will fill up.   Does the vented loop work because the head pressure of the grey water in the run from head to loop is not as great as that coming from the seacock?  Any experiences are greatly appreciated.   Thanks
 
Steve
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