Noob chronicals - plumbing questions

[SaltyDog143]

Thanks reefwars, pretty sure I know who you are now, lol.
This had me baffled (pun intended) as to how I was doing this now its so obvious I feel dumb, lol

Was wondering how do I keep the drain line in the water and still get the sock out later for cleanings... this is why I ask noob questions better to look like a fool now than look like a fool later AND have to fix something stupid.