Vents on the top of pontoon logs

[jimbob1947]

I have an old 1991 Aqua Patio - 24 ft pontoon. It's been in a marina slip and never trailered except for every few years for a thorough cleaning. After 20+ years in the water, I do have some water in the rear compartment of one log and intend to pump it out. It rides about 2 inches lower in the water than the other side and when I last had it out, I could hear a bit of a 'slosh' as I stopped the trailer on a ramp. I have a pump, but want to know if anyone knows the size of the hole in the vent. It appears the vents have plastic 'caps' on them (each compartment has a vent cap - 3 in each pontoon) and I'm assuming they will screw off so that I can insert a small hose to pump out the water. I'm thinking of using a small sink/toilet supply line since it is somewhat rigid and should reach the bottom of the log without curling. I just want to make sure the hose I buy is small enough in diameter to fit thru the vent. Anyone know the size of these vent openings? Needless to say, I haven't pulled it back out of the water and tried to remove these caps yet. I was trying to get everything ready and have the correct supplies before I start on this 'project'..
The vent caps (plastic) did screw out pretty easily and the 1/2 inch supply line hose fit just right. Only problem was the the cheap 'drill pump' that I had didn't work well, so now I'm going out to purchase a decent DC pump and try again using my hot-pack charger as my power supply.