There are so manypeople I have talked to with the same problem and you will see tons of posts on here about this. When you have 2 engines vapor lock on you oin the Ohio river and you have your family aboard it is a dangerous situation and i vowed will never happen again. Mercrusier offers nothing but a "Yup we know" try this, try that..
I even run (2) blowers.. Merc wants the mpi motors to run at a certain temp. but then in another right up they don't want the fuel to get that hot beause iit can cause a vapor lock.. DUUHHHHH... so I'm running the returns back to the main fuel fill... will post pics when done..

So silent lucidity you are going to use two of the 2" tee's? I have twins also ,i thought you could run 1 tee 2" and tee the two lines into that

No I talked to CP Performnace and they say don't run 2 fuel lines to the one bung.. Per their idea I bought (1) 2" coupler with a fuel return line bung on it..
I then bought another 3/8 female NPT s/s bung.. I'm taking it to my local machine shop to have them drill and weld the other bung on it.. That way their is no flow restrictions.. I always use S/S braided lines with AN fittings.. Cost more but so much better and easy to check, remove, tighten whatever.. Like they say set it and forget it...

Ok that sounds good ,I will do same thing

YIKES,, all the fittings and braided lines was about $231.00 to do two motors,, Will take pic's when done for future use if anoyone has to do the same CHIT to there water scooter. Hope worth it... VAPOR LOCKING BLOWS A_S....
Used to crack me up when you idel out of a dock with 20-30 people watching and somone says " GET ON IT" so you lay into the throttles (nice and smooth) and sounds goooooooooooood them POOOOF-hack-hack dead in the water... WTF.

Why use expensive braided lines and associated fittings for return lines. Just use good premium pressure fuel line hose and pushlok hose fittings. Save the dollars and use them on added performance items or extra fuel to keep boating!
JMO

Best Regards,
Ray @ Raylar

Only because I like to do it then ***** about it at the same time Just habbit I guess,, have always used and like how they seem to work with no issues and easy to take apart and reuse again later.. It ended up about $223.00. for everything to do both motors when said an done.. (and some blood and sore body parts..... For us basic gargae guys just not sure of all the options available that work.. But hey it looks pretty....