I had been using 10 liter buckets for my 2BM, which is not large enough to wash a car. So I had to refill with water half way through.
There are 2 problems with this approach. One, it isn't very efficient, and secondly, it used to waste a lot of shampoo, as I had to pour the shampoo everytime, I filled it up with water, or it would be very diluted.
Enter 20 liter buckets
I bought these 20 liter buckets, that Matt Moreman highly recommends. Although, I use the 2 Bucket Method (2BM), I got 3 buckets. One for wash shampoo, one for rinse and one for pads and brushes for tires.
I washed them thoroughly before I get to play with them over the weekend.
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The next step is to get Grit Guards for them. And hopefully, at some stage, I will try to get dollies for them.