Toilet that doesnt suck and gurgles when the sink drains

I am just at my wits end toilet number 3 we tookthis one off again checked for a blockage there isnt one. but it just wont suck it will eventually drain the water but no vacuum also ok i did read other post on other questions maybe a vent problem but my toilet gurgles when the sink drains please advise
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replying to smaloney555, Iggy wrote: Yep, sounds absolutely like a Vent Line that's blocked. Whenever you flush you're likely emptying the sink's trap, you won't hear this since the toilet's volume is so great and it will just instantly evacuate the sink trap in a big gulp. But likewise, when the sink's used it's trying to breathe through the toilet (rather than the vent), but you hear the toilet because the sink's volume is so minor and only sipping through the toilet. You need a plumber to clear your lines, it may be a bird that tried or is trying to nest in the pipe exiting the roof.
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