I've noticed, that my muffler tip flappers are not doing too good of a job. When a wave comes from the back, the boat initially rises, then falls. Upon the falling motion those rubber flappers open up and water will go up in the tip. How much, i don't know. I do also have the inside tip flappers. There are brand new and in good shape I would think those would catch whatever is remaining. Should i change something here, or go with it?

External flappers are pretty worthless. They always float open. The internal flappers should be fine keep water out. Most people don't even have the external ones.

The external ones are more just for keeping splashes out, at least in my opinion.

On my boat, my old swim platform was about 6 inches above my exhaust tips. One year on the 4th of July, I had my boat tied up at my dry rack waiting to get pulled out and the swim platform was going about a foot under water from all the cruisers running up river after the fireworks. We thought for sure the damn dock was going to break loose! Anyhow I thought for sure I had gotten water up the pipes and into the manifolds. Went down the next day and pulled the spark plugs out, no water. Cranked the motor with no plugs in it, no water and I was happy as hell.

Another story, the beach where we hang out always has a bunch of jack-offs on jetski's sending waves into the back of the boats. I watched my pipes one day and you could see when the tips went underwater, the air pocket in the pipes kept water from going too far up them, that was before I even put the external flappers on, no internal ones. After that I quit worrying about it and just put the external ones on to keep the splashes out.