Thanks for the link. I see you eventually used a piece of flexible waste pipe connected to a P trap. As well as requiring the flexibility of the waste pipe to allow me to raise the bath to fit the trap, then lower it into place, I also have the complication that the waste fitting on the bath is high up and so the trap I have purchased needs to be lowered by installing something between the bath waste and the trap. You don't appear to have had this issue although it's difficult to see exactly what the other end of the flexible pipe is connected to as it appears to bend downwards. I would have expected your waste pipe to run horizontally between or through the joists to the outside wall, so not sure how the end of the flexible pipe is connected to your waste pipe, possibly using an elbow?