Drill hole before or after?

[markyyyyyy]

will be installing a kitchen and need to drill a new 40mm waste pipe hole through the 9" solid wall + insulated plasterboard

Is it best to do this before installing sink waste pipework, or best to install the sink traps etc and mark an exit hole once the sink waste is all linked up?

ie. drill the hole at the very end of kitchen fit. I will be fully remoing the back panel for the sink unit so i'll be straight onto the plasterboard from under the sink

 

[CBW]

Probably best before, if you do it afterwards and there’s an issue, then it becomes harder. Just need to measure it out.

 

[markyyyyyy]

Probably best before, if yor do it afterwards and there’s an issue, then it becomes harder. Just need to measure it out.

How would I know where to put the hole without having the waste in place? Just don't want to mess it up.

 

[Harry Bloomfield]

How would I know where to put the hole without having the waste in place? Just don't want to mess it up.

Get everything in place temporarily, so as to be able to accurately mark the position, pull it back out and drill it with plenty of space to work in.