Hi All

Sorry for the delay in replying. Looks like my only option is to put an anti-siphon valve inline somewhere.

My setup is as follows. It is an upstairs bathroom and the sink waste goes in a stud wall, down to below the floor then essentially a straight run of around 4 or 5m and then into a vertical soil stack down into the drain. The only viable place to add the anti siphon valve is on the straight run. If absolutely necessary I could put it next to the trap but access is difficult and I don't believe the pipe coming out of the wall is long enough to fit valve then trap.

I have a few questions
1. Is an anti siphon valve likely to solve the gurgling problem?
2. Will fitting it on the straight run work ok? If so assume as close to the trap as possible as opposed to the soil stack end?

Thanks

Lee.