Blocked toilet - now after flush nearly all water exits

[Murmansk]

I've not had much experience of blocked toilets I'm glad to say - solving them has been limited to pouring a bucket of water in from a height or using a plunger.

I had to do one recently that was really badly blocked and I used a drain unblocking hose attachment on my Nilfisk pressure washer.

The strange thing is that once it was unblocked, when I flushed the water level ended up much lower than normal and there was a kind of "motor boat" burping sound!! Now even after a few flushes the water level always ends up a fair bit lower than it should be.

The toilet is ground floor, goes sharp right after pan, along half a metre, then sharp left then through some kind of boxing in and out through a wall 23 inches thick to emerge below ground level outside where it joins the soil pipe from upstairs.

Background: we just had some professional drain jetters in as the pipes were blocked by sand (seaside location!).

[Dave W]

If you're saying that the water level ends up below the level of the U-bend, perhaps the U-bend has been displaced, or a hole has been created in it, effectively lowering it.

Another cause of low level is if the exit pipe goes very deep and has small diameter, so that the falling water sucks water out of the U-bend.

[The Natural Philosopher]

supposed to have a stack vent or Durgo to stop that

[Roger Hayter]

If there is a long horizontal pipe to the vertical stack there could be a blockage in that pipe. Might have to remove the toilet and rod it.

[Brian Gaff (Sofa]

Yes I've seen siphoning like this before. One of the holiday flats we stayed in in Guernsey had this problem. Successive plumbers had no luck with it as the owners told me, so could it be in this case that the pipes are now clearer than in living memory and the true design issue is now apparent? Brian