Havent had to go to the laundromat for anything yet. ours is a queen down comforter. fits just fine, could get a king in if we had to. Guess it depends how thick the item is. Down is easy to compress and once wet its like half the size.

Indeed. I can't image in King in the T1 dryer

No issues at all for me with a King size down comforter both washing/drying.

I use the down caps for the wash cycle and the detergent works great. For drying, I dry on the pillows cycle. It's usually helpful to run it through one dry cycle, take it out to fluff/rotate and run it through a second dry cycle.