Drilling 40mm for shower waste

[SparrowHawk99]

I'm having to drill through stud as alternative is drilling twice as much through concrete which I don't want to do. I have a holesaw kit but the depth of the cut only goes as deep as the depth of the cup and I need to drill 4-5 times the depth. One option is to drill, notch out a bit of material, re-drill and so on, but is there a better tool and what is it?

 

[SparrowHawk99]

Flat wood bits only go up to 32mm by the looks of it

 

[Dean744PiN5]

Fostner bits are good for that, screwfix do a set will have the size you need
http://m.screwfix.com/p/forstner-bits-16-piece-set/83345