Here is our disposable pastry bag (a.k.a. cake decorating bag) loaded with structural epoxy. Today I'm using the smaller Wilton #10* plain tip.
The metal tip is held in place with a plastic coupler. You slide the main part of the coupler down in the bag, then cut off the end of the bag, just enough for the tip to slide through. The metal tip goes on the outside, over the plastic and the coupler, and the nut from the coupler screws on to hold everything in place. The nut threads capture the edge of the plastic bag.
You can reference YouTube videos showing how to use a pastry bag. The Pioneer Woman's website has the following advice: 'Don’t substitute a ziptop bag. They’re unwieldy, they explode, and they’re not the right shape or size.' I heartily concur: I was able to continue pushing the structural out of this bag even after it had begun to stiffen. That's a good bag!
The tools cleaned up nicely in acetone. I removed the coupler nut, then cut the bag to free the coupler and metal tip. I scraped out most of the structural, and dumped the parts into an acetone bath.
I spent a total of $7 (on sale) for 12 disposable bags, the coupler and two pastry tips at Michaels (craft store). As airplane tools go, this may be the best bargain, ever!
*Note: I have read that the tip numbers are not consistent across manufacturers. I'm using the Wilton brand, is a common supplier of cake decorating supplies.