I have used a couple different methods for fulling:
1. Bucket and plunger. This works but it's a great big pain in the *** seriously. Takes like 2 hours to do what 20 minutes in a washer does. And that's with super-hot water, vinegar, home-made lye soap, the works.
2. Washer/Dryer. Unless your item is in a bag of some sort, like a pillow case, I DO NOT recommend placing towels in the load. Another pain in the *** is getting all the terry cloth pills off the item. I have again used super-hot water, and also lukewarm, and honestly, there was no difference. I have continued using the lukewarm (almost hot, maybe 110 degrees like to activate yeast-a reference for all you bakers) from the tap, and use a very small squirt of dishsoap instead of laundry detergent since it seems to make it a bit "stickier" or doesn't leave any softness in the water. Does that make sense?
I put the item in by itself, on the smallest cycle, and I even let it go through the spin cycle (didn't know not to!) with no ill effects. Then into the dryer it goes. I've had decent results with this method, nothing has fulled too much, but I think it depends on your stitching beforehand too. Like if it's real airy and full holes it would full more than if it was stitched closer, like how it would be done if you weren't fulling it. Does that make sense??
3. Lastly, I have used a textured cutting board (read it somewhere, decided to try it) and rubbed the item against it (like one would with a washboard) and it did seem to have some effect, tightening the area I was rubbing/scrubbing a bit more than the rest, but that was another pain in the *** method... Maybe if I had a real washboard?
The major recommendations I would make:
Make a test swatch.
Use shampoo, dish detergent, or body soap instead of laundry detergent (to strip the fibers of natural oils better and allow more tangling).
RELAX AND ENJOY!! Even if it turns out unexpected, it's still one of a kind!!