Mercruiser carb question

I don't know if this is the right place to ask due to the fact that I drive a fakeboard boat, but you guys have been awesome and helped a ton so far. I have a 97 Maxum with a 5.7 Mercruiser and when I go to the lake It usually starts pretty easy the first time, but every time we stop for more that 2-3 minutes I have to fast throttle start it. The carb was actually just rebuilt a couple months ago. Anyway, today I am looking at the motor and see a yellow/clear hose attached to nothing below the carb. I take off the fire arrestor and on the back of the carb there is an outlet with nothing attached. Just wondering if this may be the source of my issue? I hooked it up made my fake lake and it fired right up, no throttle pumping. Then after about 5 min I shut it down and came back out to try again. It hesitated a little but ended up starting. Just dont want to hook something up I shouldnt have, but it definately looked like a fuel line and went on the fitting like it should be there. Just curious what some of you may think.
Thanks

That clear yellow tube should connect between fuel pump and carb. It's in case the fuel pump diaphragm ruptures fuel will vent through there into the carb and not into the bilge. Port on back of carb may be a vacuum port, should be plugged if not connected to anything. (generally no vacuum lines of a boat, occasionally will have one for PCV valve).

Problem with having to give lots of throttle to start when hot is an indication of flooding. Remove flame arrestor and run engine to temp. Look down barrels and see if you see any fuel dripping from the boosters (rings in the carb barrels) while idling. Shut engine off and observe if fuel drips down the primary barrels of the carb. I can almost guarantee there will be some fuel dripping and you will see the throttle blased and venturi get wet. This causes a rich condition and no start unless throttle is opened enough to lean the mixture.

This problem is most often caused by float height too high or a needle and seat that is not fully sealing. You need to find the spec for your carb float height and check it. Also remove needle adn seat and clean/check. Replace if necessary. Also ensure the guy who rebuilt the carb did leave out the black plastic spacer jobbie on top of the float/needle/seat assembly.