I think this might be a silly question...but I don't know what I don't know....
Is there any reason the high point of the exhaust (post muffler) to the outlet can't be a shallow slope? I am redoing my exhaust system (and engine, and...) and the existing system goes from muffler, up a bit, over the fuel tank, up further, and to a high point that comes close to straight down to the exhaust thru hull - essentially irregular but shallow slope from muffler to high point, to steep slope to exhaust
I'm thinking of changing the system to a vetus NLP50 that would go up a sharper slope directly to a Vetus NLPG50 and then to a shallow slope to exhaust thru hull.
I don't see a reason moving the steep slope from before the high point to after would matter, but I thought I'd ask. The high point would be very close to the same height and same distance from the center line.
I was limited by the cockpit sole and aft deck (my highest point) in my installation. I made sure I installed a waterlift muffler with plenty of volume for the drain back of my 2 3/8" exhaust hose(easy to calculate).
In theory, the exhaust hose could drain back it's entire volume in seawater, at engine shut down.
In practice, I've found surprisingly little seawater (opening the drain to actually see), is in the line at shut down.
The flaw in a system like this is the possibility of cranking the engine so long, you fill the system with seawater. Again in practice, I don't think the battery would hold up long enough to pump the (a very small amount during cranking) amount of seawater needed to fill my oversized waterlift muffler and hose to above the riser, and into the engine.
My exhaust outlet is 12" above the waterline, with the high exit bend in the hose, 12" above that outlet. I'm not worried about backflow into the system. It's worked better than I expected after a couple seasons. My raw water has a vented loop 12+" above the riser which is wrapped in exhaust insulation.
Hope this helps.