Grey water flowing back into toilet at the end of the system?!?

[Brady H]

help/advice required...
two toilets on the ground floor, when the toilet furthest from the soil stack is flushed, the toilet nearest the soil stack (right next to the soil stack) collects waste matter in the toilet bowl. Neither toilets are low flow (modern systems) both ball cock old school toilets but the soil pipe connecting the two has the correct amount of fall per meter etc... there is a slight angle in the soil pipe before it hits the soil stack, I'm wondering if there may be a small blockage here causing matter to hit and back fill the toilet bowl right next to it? How would I investigate this without having to take the toilet and pipe out?

neither toilets are blocked and do not fill up/block when flushed, so this is a little more than confusing for a novice/DIY'er. the manhole outside the property has been well inspected, toilets flushed all at once or separately can be seen flowing well via both the manhole and inspection chamber nearby. No external blockage apparent.

Any advise would be appreciated.

 

[ShaunCorbs]

Might be an air problem is there a vent on the long run ?

 

[FK Toilet]

I have a similar problem but the waste goes from the toilet closest to the stack to the one furthest from it only. We have consulted with some pumblers and they believe it could be a problem with out pipes inclinations, but we are not convinced at all. Air and vent does sound as an interesting potential problem, I read in another forum that it could be a poor venting where air is let in and pressure is built up.

If anyone has any ideas about these issues please ket us know as we have received ridiculous quotations with potential reworks including even lowering our downstairs room ceiling.