Sorry for the NOOB question, but why aren't these line shorter to begin with? Why are they routed to the very bottom where the water is?

Because the hose is long enough to cause the engine to stall before the water gets to the carb???

I ask because I just melted my vent hose on the right side after jetting my carb last night and putting on a Q4 slip-on. I was eager to start the bike and couldn't see really well where I rerouted the vent hoses because of it being night and all.

 

It's common practice to route the vent hoses down very low. These lines will dump fuel on occasion, such as a tip over. We want this fuel far from the engine, spark, hot muffler, etc.

 

It's not a theory, it happens:

https://www.kawasakiforums.com/forum...ossings-43530/

Plastic will be fine, you don't need brass.