Two storey drainage gurgles??

[Ronaldo451]

We have a two storey house with bathrooms on both levels. Lately the downstairs toilet has started gurgling and having the water sucked out of the s bend when the upstairs shower is running or toilet is flushed. This does not happen all the time but a few times per day. Occassionally the downstairs toilet also backs up when flushed and takes a few minutes to drain back to the right level.

I am not sure if these two issues are related or not.

I noticed the surface water of one of the two outside gulleys was caked over with a hard surface and thought this may be affecting things - if the pressure or vacuum created by the upstairs water running down through the pipes had nowhere else to vent or draw from perhaps the downstairs toilet was the only alternative source?

I cleared all the scum and muck out of both gulleys (350 mm of putrid, swamp odoured silt - gulleys are at ground level with no 'collar' and apparently lets in debris when it rains) and was hoping that would be the end of it, but we still have 'moaning Myrtle' in the toilet!

Any thoughts on possible causes and solutions would be appreciated.

[bricks]

In-correct venting of the downstairs fixtures.

[wonderplumb]

If its started lately you might be in for a blockage, it sounds like its partially blocked already. Imagine a 4" pipe, partially blocked to say 1 1/2" or 2", waste water runs down the pipe as per normal, hits the partial blockage and as as it pulls through the smaller diameter it creates a vacuum behind it, tries to pull air from the easiest place it can in your case being the downstairs toilet hence the gurgling. Sounds like the junction to the branch drain serving your downstairs fixtures could be the problem. The Shire is a specialty for it as every one likes their trees etc.
But before you get too carried away climb up and check the vent isnt blocked, I went to a job in Caringbah with the same problem, the old 2" sheet metal vent with a chinamans hat cowl had swallows nesting in it.