Fixing a gurgling sink

[qprfact]

Hope someone here can help! We've been in our current house for just coming up to a year, and we've decided we really need to sort out a perpetually gurgling sink (well, it seems like that) in our en suite.

After water has drained from the sink, it gurgles for quite some time before dying down. I think it's down to the length of the waste pipe. The pipe goes straight down almost to floor level, then horizontal with floor before going out (see pics).

Reading elsewhere suggests fitting an anti vac trap, so I went and bought one yesterday, but looking again at the underside of the sink it looks very much like an anti vac trap is already there!

I've also seen other references to something called an air admittance valve - is that what I need and that would work for me?

Thanks in advance?

[stoneyboy]

qprfact,
Yes get an air admittance valve and fit it as close as possible to the sink - after the trap.
end

[BuyersAssistant]

That looks like an extremely long pipe for a sink. I'm no expert, but I don't think that they are normally that long. Normally they connect into the main waste pipe much nearer to the sink.

I could be wrong.

Possibly because it is so log, it is dragging a lot of air in when it empties.