Toilet Flushing problems

[Happy_Harry]

Three weeks ago all of a sudden 2 out of 3 toilets in the house had problems clearing the water, it took about a minute to drain the water, the other thing I noticed was that the residu of water (at the bottom of the toliet)looked to be lower than normal. As this happened after the Mrs used a fair amount of limescale remover and cleared a lot of limescale I believed the blockage was caused by lime scale that was released from the toilet. I used half a litre of lemon juice and left it overnight, the next day I flushed and everything was working fine again.
Now, guess what, problem has reoccurred two days ago.

So, to summarise, we have a septic tank, we have 3 toilets , 2 of which seems to have problems, one shower seems to have a problem as well. None of the sinks or the bath appear to have a problem. The pipes of the 2 toilets don't seem to be connected.

Any ideas what could have caused this and what can be done ?

 

[REXO]

Are the discharge stacks from the toilets vented? If the builder hasn't installed vents on the pipework then this will cause siphonage of the water out of the toilet bowl and lowering the level after flushing.

 

[elcato]

I'd say you have a blockage. Have you lifted any manholes outside to check for a blockage (assuming septic tanks have the same access pipes as the city sewers) ?

 

[Happy_Harry]

Thanks Rexo, actually now I come to think of it.. I believe the only vented pipe is of the one toilet that does not have a problem. I will doublecheck when I get home tonight, but what I don't understand is how come we lived there for 8 months and only now it becomes a problem ?