Thanks for the comment Amador. I think it has merit.

I based my tube on the same idea as used in steam engines. In my steam engine the exhaust vapor is discharged into the boiler exhaust tube, but flowing up instead of down. It works a charm, and there is no slanted cut on the tube. However, there is certainly no propwash!

I can reach the end of the tube, and file a slant cut on the end. I will do this and try it again. But first, I think I will run the engine with the drain tub hanging in free air as before just to see if the engine gains back the lost RPM, which will confirm our suspicions.