Re-Routing Bathroom Waste

28 Dec 2007
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United Kingdom
I was looking for some advice regarding bathroom waste pipes, I am ripping out an old bathroom and replacing it shortly, Its a small bathroom however to accomodate the new bath suite the toilet and sink will swap positions (the bath will be L shape so the toilet would foul on it if not moved). The soil stack sits internally in the bathroom corner, boxed in, currently the 4 inch waste from the toilet is above the floor and goes directly into the stack via a 700mm run of pipe, the sink waste goes under the floor and the bath I presume goes directly into the stack as its right next to it.

My plan was to re-route the 4 inch toilet waste into the floor, because the toilet and sink will be installed in a vanity unit, this will avoid the pipe being on show at the end of the vanity and prevent butchering of the vanity unit. The run of 4 inch pipe would be around 1.5 meters and in between the joists I have around 180mm gap so enough fall for it to work.

In my head this all works the only grey area I can think of is when it comes to connecting the new 4 inch pipe to the stack, it will be lower and a solvent weld fitting or one of the other waste pipes might prevent me drilling a hole and connecting it using a boss?

Thanks in advance for any advice.
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Here's a top down view of the planned new bathroom, currently the bath and sink are in opposite positions.

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