Trace around the PVC pipe on the outside of the tub. Use a soldering iron to open out the hole from the center to the inside edge of the tracing ensuring a snug press fit.
I used some plastic end caps for the pipe and drilled a hole in the tub and then a hole in the cap and used a rivet to hold the cap in place inside the tub.. That way I didn't have to worry about to much humidity escaping as well..
Buy two rubber ends or four cut the pipe to the corner to corner then put the rubber ends on the pipe an push them in so they are wedged slightly that way when u want to get him out u just lift the perch if u screw it then u have a problem to get him out to clean.