While excavating, we realise that the sewer line was running very close to our extension. We thought I would be a good idea to installed a toilet into the room and bathroom too if possible. However the sewer line come just above the top of the slab where we would have joined in to go inside the new room for about 4 metres.

A
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X--------------B--------------------------C

The above drawing shows A Existing upper toilet. X is inside the new room where the new toilet will be. B is where we want to join into the sewer line. From X to B there is about 4 to 4.5 metres. Point B is where we are just above the slab level.
From B to C there is about 8 metres with a drop of about 300mm.
If we could drop point B by 200mm we will then be below the slab level. If we could have a fall of 50mm from X to B we will propably be OK.
Is the 50mm drop from X to B and 100mm drop from B to C OK. Or do you have a better suggestion?
Regards Nicolas

Good morning Nicolas, You would have made it a lot easier for this Florida Cracker to compute length and fall if you had presented your problemi in feet and inches. However I managed to convert after a fashion. Point "X" to "B" works out to about 14' which giving it the stardard fall of 1/8" to the foot would give you a fall of 1 3/4". 50mm of fall should be plenty. You have plenty of fall left over from point "B" to "C" so you're OK there. What I don't see mentioned is your plan to vent the toilet. You do plan on a venting this don't you? Also if you add any more fixtures be advised that you're going to run out of fall. At 14' to the center of the closet bend you will only have about 1 3/4" of fall to work with using 1/8" to the foot.. 50mm works out to a little less then 2". That means any fixture must tie in not over 2' from a side inlet on your closet bend. You're OK with the fall on the toilet. Add a bathroom group and I'm afraid you'll run out of pitch Hope this helps out. Tom.