I use the three line system on my cowled in engines. If the muffler is also cowled in, I put a tee in the muffler pressure line and run it to a second fuel dot. Then when fueling the plane I connect an overflow tank to the second dot/line. In this way excess fuel goes into the overflow tank with very little going to the muffler. I currently have 5 planes set up this way and it works great.

Bruce