Guys, thanks for all your input. I thought you might like to know what I have eventually gone with.
Given the space and access I have available and the some of the issues raised by Madrab (especially spillover levels and the constant incline) I have dropped my own idea of a vent pipe and gone...
Thanks Madrab, I think we're getting close, but not quite there.
Re the AAV suggestion. To keep things simple I haven't yet mentioned there will be a basin on another tee between the bath and the shower tee. I plan to fit that with an anti-syphon trap to prevent it (the basin) being pulled by...
Steelmasons : my industry has gone to the dogs too, which is why I can't afford to pay a plumber and end up struggling to do it myself :) .
I sympathise with your industry problems, but am not sure whether it's your industry that is making you weep or the suggestions of this particular...
I am completely relaying out my bathroom, ie gutting and moving all fittings to different locations. Many of the waste runs have to go under the tiled floor, so I will be using solvent weld wherever possible.
I have three alternatives for my shower waste.
1) To run it into an old push-fit...