So I did.
It's definitely not professional, but I think it will do the trick and it only cost about $5 to make.
You can make one too. Here's what you need to make two wet bags:
A 3-gallon trash can with a lid
3/4 yard of PUL fabric (It was in a special cloth diaper section at Jo-Ann's)
Nylon cording (cheap, in the hardware section of the grocery store)
2 cord stops (found in the notions section at Jo-Ann's)
a safety pin
bag clips (so you don't penetrate the waterproof fabric while you hold it in place)
Please note: you may need a different amount of PUL fabric depending on the size of the trash can you purchase.
1. Measure your trash can around. Mine was 28 inches so I decided to make my bag 32 inches wide. I learned the hard way after my first attempt at making a bag that deeper is better, so although my can is only 14 inches deep, I made my bag 25 inches to leave room for the casing and to be able to fold it over the side of the can to hold it in place. End measurement: 32"x25".
2. I made French seams so that the bag would be more waterproof. Pin the 25-inch seam together RIGHT SIDE OUT and sew using a very narrow seam allowance -- less than 1/4 inch. Leave two inches unsewn at the end. This will be the top of the bag because you'll need the sides free for the casing and cord.
3. Turn the tube inside out and using the bag clips, clip the seam to hold it in place. You are essentially pinning it in place but without having to penetrate the waterproof fabric.
4. Sew along the side again, this time leaving about a 1/2-inch seam allowance, again leaving the top two inches unsewn. Pull the fabric slightly as you go. It's a little sticky and has a hard time feeding itself through, at least with my machine.
5. Do steps 2 and 3 with the bottom edge. You should now have something that looks like a bag.
6. Now here's the kind of ghetto part, but I don't really care. With the bag right-side out, turn in the unsewn edges of the top and sew them down. This will ensure you don't have any raw edges for the cord to fray up.
7. Turn down the top edge and pin in place, making a 1-inch casing. Sew all the way around the top of the bag. The wider the casing, the easier it is for the cord to move around. If you wanted this to look more professional you could turn down the top edge just a little bit and then turn it down again to make the 1-inch casing so you don't have any raw edges at all. I just really don't care that much!
8. Attach a safety pin to one end of the nylon cord and feed it through the casing. Leave about 6 inches of cord on either end. Use a lighter to melt the ends of the nylon cord to prevent fraying.
9. Thread the two ends through the cord stop.
10. Place your new bag in the trash can and wrap the edge of the bag around the can. Use the cord stop to hold the drawstring in place around the can.
11. If your pail starts to get stinky just drawstring the bag so odors won't escape as easily. When it's time do to a wash, just turn the bag inside out as you dump the diapers in the washer and toss the bag in with the wash. The PUL fabric can be washed and dried just like the diapers.
So we'll see how well this holds up. At least I saved a bunch of money by making it myself and that makes me feel goooooooooood!