[C320-list] Seacock question

[SV Osprey]

I am in the process of removing my marine head and replacing it with a composting one. It’s going to be done in stages so my first order of business is going to be disconnecting the head from the intake through hull. Should I cap the through hull off or can I leave 6” of hose connected and plug this off?  The seacock services another hose so I cant remove it now (not hauling the boat). Can anybody recommend a hose plug source or type of that is a safe choice? It 3/4” I believe. 

Elan
Sv Osprey
1997 Catalina 320 #451