After closing my pool the first year I realized it was a pain to blow out the lines. So I looked though the plumbing section at the local home improvement stores to see what I could rig up.
What I ended up doing was to use pvc union connections for connecting the skimmer lines and return lines to the filter and pump.
I store the pump inside over the winter along with some of the piping.
With pvc unions everything comes apart easy in the fall and goes together easy in the spring. Occasionally I need a new o-ring.
To blow out the line I bought an extra unit and use half of it, a short section of 1-1/2 pvc pipe glued to the union and a 1-1/2" to 2" flexible couple to attach the pvc pipe to the shop vac hose.
Now everything is held together well and the hose does not blow off. You don't need two people to blow out a line.
I also bought a few extra union and pipe plugs to cap the skimmer line, return line, and inlet and outlet on the filter.
Also makes it easier to pour in antifreeze into the skimmer and return lines now. When I installed the union I made it so they were all vertical. You can out them horizontal and make you blow out adapter with an elbow to make pouring in the antifreeze easier.
It's a little work installing the unions but you only need to do it once. And any leaks I end up with in the spring are easy to fix with a new o-ring.
This is not screwed together tightly. My other union for the return line is the other half so I need to change it when blowing out the return line. If you think ahead a little further then me you won't have to do that.
The flexible rubber coupling (No-Hub) is for 2" pipe, the union and pipe is 1-1/2". So you could use a 1-1/2 x 2" flexible coupling.
Once the hose clamps are tighten the shop vac hose does not come off. If your hose does not have a lock onto the shop vac you will need to figure out how to secure it so it won't.