Your tank has a pickup line with a clunk so the pickup follows the fuel at the back of the tank. The other line is the overflow and goes to the top of the tank so that when the tank is filled, that line will overflow when the tank is full. Since the muffler pressure has to get into the tank somewhere, you gotta hook it up to that overflow line.

You could add another line but why not use the one already there for the muffler pressure. After all, it works ok. Well, that's not always true, as you've proven clearly.

Uniflow is a way to get a steadier run from our systems, but it takes an additional line for the pressure. It works steadier by placing the outlet for the pressure into the tank close to the pickup, where the fuel is drawn from the tank. Cut down the distance from where the pressure enters to where the fuel exits, and less things are between the two important locations. There will almost always be solid fuel, and not very much of it, between the pressure in and the fuel out, if there isn't much distance between the two.

So how do you plumb a Uniflow? You run a 3rd line. It'll run from the muffler fitting almost to the pickup clunk. That pressure line can end within about a half inch of the pickup clunk. The line can just end. It can be connected to the pickup line or the pickup clunk. Or it can end as another clunk. (They will both follow G forces and stay pretty much together.) That is what the 3rd line will be. And you'll plug the overflow line except when filling the tank. And you can fill from either the pickup or the pressure lines.

Is it worth the trouble and bother? It's up to the builder/flyer. Depends if your particular airplane/engine/tank/plumbing is giving you trouble or if the flying you do needs a steadier fuel feed.

BTW, I just refitted the plumbing on my H9 Thunderbolt from uniflow to "simple 3 line". The airplane now loses just a bit of RPM over the top of loops etc. I'm going back to the uniflow layout next time I have the cowl off. I don't fly the P47 in precision but I don't really like the slight loss of power. Fueling the plane with a uniflow setup had a problem with siphoning from the layout of the lines inside that cowl, and that was what caused me to decide to try the simple 3 line. It wasn't worth it.

We all decide what's worth the trouble and what isn't. And sometimes have to choose between one bit of trouble versus a different bit of trouble. With uniflow, we have a solution to one bit of trouble.