En-suite bathroom plumbing.

w/c's should be fine, need to be vented somewhere though.

Ideally, run separate shower and basin wastes. Pipe sizes need to be 32mm basin and 40mm for the shower.

If not, try and increase the common pipe run (where they join up) to 50mm that would be good, otherwise 40mm should be ok provided the run is not too long.

Your pipe fall is all important, water doesn't flow uphill. Make sure it goes downhill all the way, no flat spots!

 

I've just done something very similar for a client, basically split the main bathroom into 2 to create 2 shower rooms, one of which is an ensuite.

Here's a pic of the soul stack. You don't want too much fall for a soil pipe as this can leave solids in the pipe as the water rushes over them. Sink and shower wastes combine internally into a 50mm pipe which is inline and behind the main down pipe. As both showers are off the same pump, there is no problem with flow.

 

Had a prob posting pic. Soil pipe was originally cast iron, but easier to replace whole lot with plastic.

 

My service handbook is giving a fall of 9mm/m for WC branch pipe for a single stack system.

So not much of a fall.

 

Prob best to put a new run of 50mm waste if possible and yes, put anti vac traps on...certainly can't hurt

 

50mm everytime for a shower nowadays, the newer showers can put out a lot of water in a minute, for example Mira shower low profile trays have 30ltrs maximun flow rate a minute, some other makes of trays, have flow rate of 54 litres per minute,depending whether shallow or deep, so 50mm pipe is essential.
You can tee the basin 32mm pipe into the 50mm pipe, easy to get 50mm shower traps.