I've been making some dry bags and flotation bags lately. One advantage of DIY is that you can build a flotation bag that will really fit the boat.

(Thanks to Tom Yost and Chuck Holst and others for good web info this topic.)

I've been using two different materials: heat-sealable fabric and inflatable boat vinyl from the local plastics supplier.

Performix Vyna Bond adhesive is fantastic for vinyl and will also glue vinyl to the fabric if necessary.
It will also bond thin ABS sheet material to a dry bag if you are using a fold-over/roll closure and need a stiffener for the top edge.

(I don't have a good local source for HH-66.)

Twist valves were from NRS - pretty cheap and seem to be the same as on my commercial flotation bags.

I did some experiments gluing the vinyl tube directly into the flotation bag hem and I didn't like the results (leaky, weak).
I really wanted an elbow fitting of some sort, anyway.

One option is a 90 deg thru-hull from a marine supply place. Pricey, and too large for the hose, so you'd need to do the hose-inside-a-hose thing to adapt.

Browsing around the local 'home improvement store' aka HomeDepot, I started in the electrical dept.
I found a 90 deg. plastic fitting for attaching flexible conduit to a box.
This will work (see pic) but needs to be adapted to the smaller hose. Also costs about $5.