Best you can do is get a couple of elbows to make the "U", since your using tubing it sort of limits you to barbed fittings.
If you want to get creative you can try to find some solid PVC fittings that you can snugly put the tubing into, and glue it in place. that will result in a smaller more compact "U".
all kinds of ways to get creative here
dr_sudz .... I have already called Python, and done all the digging to determine that the tube is in fact 5/8" ...... though the measurements (IIRC) are closer to 7/16".
believe it or not I went through about 7 people before finnally one guy comes on the phone and says "5/8" tubing, needs 5/8" fittings" (impossible to find for the most part)
Just make sure when you are finding fittings, clearly state that you are looking for x ID or y OD .....
5/8" hose has a 5/8" OD .... if you go and buy a fitting for a 5/8" ID hose, you will find the fittings MUCH too large (again.... from experience lol)