The Ultimate Car Wash Bucket from Griot's $44.99. Sounds like overkill? Maybe, but it does what it supposed to do and sure beats a leaky sheetrock slurry bucket. From the seller:
This truly is the Ultimate Car Wash Bucket. Here are five important and unique features that I think you'll appreciate... It has a lower grill so the heavy debris sinks to the bottom and won't allow your wash mitt to pick it up again. There is a molded-in measuring cup (patented design) in the grill for you to dispense the proper amount of Car Wash each and every time. No more guessing, no more wasting product. The top sieve allows your wash mitt to lay on it without dripping over the side. The 2" casters are included so you can push the bucket around with your foot if your hands are full. The heavy-duty molded plastic tub holds a massive six gallons of water, has hash marks in liters and gallons on the inside wall, and has a wonderful form-fitting handle. The bucket is 19" wide, 9" across and a generous 9" deep. The snap-on lid keeps the water from splashing during transportation. The most well thought out wash bucket on the planet. Enjoy the best!