Sealing tiles in shower cubicle

[dsuley]

Hi everyone,
I've done all the tiling in the whole bathroom over aqua panels, and I've used flexible Bal adhesive. there are 2 Stem Elbows coming out the wall which connect into the power shower.
There is a cavity tunnel around the pipes - about 30mm deep (please see attached picture) , I've left them empty for the time being so I can ask you guys for suggestions, what would be the best thing to fill it with? sealant, grout, tile adhesive, silicon or something else? what would you suggest?

Also, I've tiled all the way up to the ceiling which is covered in plaster board, what's the best thing to use for sealing the area between the tiles and ceiling?

I would appreciate your help and advice,
Thanks
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[OJJ]

If you intend to seal the gap around the pipes use silicone sealant. At the top of the tiles there is little chance of direct moisture penetration so you can use what ever gives the neatest finish. Silicone sealant can be applied neatly with and application tool such as a Fugi and will all for some movement without cracking.