The 45 was just a guess based on the positioning of the toilet in the pictures (it seemed to be more or less just the other side of the wall), you can get other bends, and even fully adjustable ones like Screfix item 77224
Adjustable Bends (Screwfix item 77224 - Floplast Push-Fit 0−90.
Concern is that these are undesirable for installation under a stud floor due to possibility of leaking. I think the thin seals in adjustable fittings are prone to fouling, losing elasticity, and leaking from slight movement. Since the first sign of a leak would be smells under the shower, an inaccessible and adjustable fitting poses a long-term risk.
Over that distance and that close to the flushing appliance it won't matter about the angle; soul pipes have shallow angles to prevent water rushing past the solids it's flushed with leaving them behind in the pipe. You're supposed to use larger radius bends when going from a vertical to a horizontal, than is presently installed in your location
Your saying that the falls are not an issues over these smaller distances? - as long as there is some fall, large or small.
As to waterless traps, they can be changed, and in some even just the membrane is changeable if it has ceased to function. I've been using Osma HepVO ones for 12 years now and not had to change one yet, so I'm confident in their reliability. Also have AAVs that have been reliable despite some measure of nay-saying regards them (the smaller diameter ones Screfix stock acquire numerous negative reviews)
Product: HepVO Waste Traps (e.g., Screwfix item 3962K).
For the sinks seems like a great idea. It is unclear if a HepVO trap can be easily accommodated in the short run between the shower plug hole and the soil pipe. While the membrane in sink wastes is easily replaceable, replacing a failed membrane under a shower, particularly with a stud floor in place, may prove difficult.
Just options. Given that you've already dug a sizeable hole you could extend the hole and the waste into the other room if you wanted to install a swept 90 at the increased floor height
Boss connections can be made anywhere in a run using Screfix item 82795
Not sure I understand this, but am reviewing the 45 degree idea.
A 45 degree bend may be feasible, but some trigonometry is required to precisely determine the pipe's final position. It would save some digging. The setup may involve extending the incoming horizontal run, then using a 45 degree fitting to rise into the WC. The pipe must pass under a stud floor with a shower on top, that is 22cm high, which also should provide adequate space for those strap on waste connections.
Air Admittance Valve (AAV) and Stub Stack
Installing a stub stack for an AAV seems highly desired as a precautionary measure while working on the soil pipe.
How can an AAV stub stack be created when using a 45 degree bend? Is it possible to install a 45 branch pipe (e.g.,
Amazon link example) and orient it such that the fitting provides a 90 degree vertical rise for a 50mm AAV pipe directly behind the shower stud wall? This would provide peace of mind and allow for future venting even if HepVO traps are used.
