Shower waste configuration

[Keithsurf62]

Hi
I'm currently doing the pre-planning for my next DIY project fitting a shower tray and enclosure from scratch. I'm confident of being able to do the job but not being a plumber not sure the best way to go about it so would appreciate any advice.
The current upstairs room has a black waste water pipe running between the joists from one end to the other where it then drops downstairs. There is currently a sink plumbed into a boss on the toilet pan connector at the start of the run. This then feeds into the start of the black waste pipe. I want to add a shower tray and plumb the waste water into the same black waste pipe just before it drops downstairs so this will be downstream of the toilet. Because I only have the depth of the joist with which to connect the shower tray waste into the black waste pipe i don't have room for it to connect into the top of the black waste pipe. Can I add a 40mm pipe boss and connect into the side of the black waste just above centre? Also is having this connection downstream of the toilet going to pull the shower trap when the toilet is flushed. Thanks in advance

 

[Madrab]

If it's not into the top of the waste pipe then yes there is a risk that the toilet could pull on the shower waste pipe, also if there ever a blockage problem in the stack then the toilet will back up into the shower, not ideal.

TBH ... I'd haver another look at the design.