Went out to figure it out, since I'm impatient. Did the drain nozzle mod while I was in there. Hopefully that fixes the issue.
Outer diameter is ~10mm, so a 25/64 or 13/32 should work.
Inner diameter was ~7.5mm, so 19/64 or maybe 9/32 will work.
I figure that since at the top of the tube, it fits around the outside of the input nozzle, having it slightly smaller is better, and as such, 9/32 is slightly smaller.
At the bottom of the tube it fits inside the output nozzle, so slightly larger is better, and as such, 13/32 is slightly larger.
I used the following chart for conversions > http://mdmetric.com/tech/cvtcht.htm
As for the nozzle mod, relatively easy to do, easier to do in the summer when **** isn't cold as well, and wirelooms are difficult to bend! I haven't tested it yet though, going to the touchless car wash in a few minutes, will report back!