I sealed mine and used easy joint select.
I'm doing in stages starting last year. Currently laying more slabs.
Lay slabs.
Sealed.
Then sprayed water and used resin with a soft sweeping brush.
Tired the best I could to compact the resin.
It's a bit stressful and many white granules spread...
You only got to cut two bits apart from the big gap.
Loads of videos in YouTube showing you how and it's very simple.
Just need a fine tooth saw and pencil. Practice with paper and scissors so you understand or make template up with paper first.
Plaster don't stick to wood very well.
It's because of wood movement.
You can fix expanding metal lath over wood or two layers of chicken wire and skim over.
You can also buy 6mm plasterboard and put over the wood. No need to skim then maybe
Maybe the float arm is worn out and fell off.
You can try to fix with new inlet rubber that's inside the float valve and clean parts and see how that works out, but I nearly always buy a new Fluidmaster inlet with brass thread.
You need to think about what's best.
The inlet connection thread...
First thing is to get some masking tape around the window to keep clean.
Top of the masking tape edge level the best you can with the side wall and top plaster.
Use purple masq tape. Probably best on market IMO.
I'd then squeeze some mixed powered filler in joint. Use toupret standard powder...
I would run a new bath pipe straight down the side of black rain water down pipe.
I do it in black..
Separate them..
You have that long drop causing suction on one or the other..
Mine was built 1964 and there is a clear plastic sheet under the concrete base as a dpc.
Then asbestos flooring tiles which was the normal, which I took up and floor looked like yours although the bitumen was very thin.
I scratched up through to the concrete and washed over.
Use 2 pack self...
Use products like patio magic twice a year and sand joints when required.
There are a few drives on our estate that were like brand new for years. Not a weed in sight.
House was sold and the paving was covered in weeds within months
Dig out bad knots or problem areas and you can use 2 pack wood filler.
Aluminium primer I used on my pine stairs as the knoting solution failed and its been fine.
Give the aluminium primer a few days to cure following spec then 2 coats of acrylic primer.
Aluminium primer is gray...
You need to rotate the central driving tab thing..
I've seen it done but never watched how.
Lock was snapped..
Then a few seconds fiddling inside it all opened..