Cartman: (explaining where he got all the "sea men" for the aquarium) "Yeah I bought all I could from this bank...I got the rest from this guy named Ralph in an alley...stupid a**hole didn't even charge me, he just told me to close my eyes and suck it out of a hose!"

*Boys are watching the semen spread in the aquarium*
KYLE: You suck it out of a hose, huh?
ERIC: Yup.
STAN: Hmm.

What did they mean? (I have my own idea what they were trying to get at, but im just making sure so if u know then post it here)

you don't get what it means?

I believe it is referring to a blow job, and the "hose" is a certain part of a male anatomy. Sea Men = Semen