We are at first fix stage and as plumbing pipes are going in we notice a lot of gaps that will need filling to stop airborne sound travelling between floors and walls. 
 

What is the best method, tools, adhesives to go about filling these holes/gaps to stop sound transfer through them, please? 

 

Thanks in advance. 
 

 

Intumescent acoustic sealant like FIREPRO from Rockwool for the smaller gaps. I'd then be cutting a crescent shape out of whatever the floorboards are but with the PROPER sized hole saws this time to go round that soil pipe and gluing / sealing it in.

You could.....cut a square of floor board. Drill through the centre with a 114mm hole saw. Cut the square in half. Glue and screw up from underneath or from above if there's two of you, can you even get to it? Fill from above and below. I think you need to fill these gaps to satisfy Parts B and E of the building regs.