What size of vent for grey tank/composting head?

[TheArgobus]

My grey tank (which isn’t really grey because of urine) vents to a 1/4” vinyl tube, which runs under the floor and up to where my in progress composting head will be. I also will have a five gallon bucket for solid waste, in its own compartment that I want vented as well. I’m planning on both vents going up to the ceiling, where I already have a mushroom cap vent installed, along with a small fan to encourage airflow in the right direction.

What size should the head vent hose be? 1/4”? 2”? How do I attach this hose to the bulkhead (where the bucket is) and the ceiling (where the 2” fan is installed)? How would I connect the 1/4” vinyl tube to this vent as well?

I’m having a hard time visualizing how to attach a hose of any size to the ceiling, and figured I’d ask the experts before I start buying things.