Hosting a dog washing fundraiser can be a lot of fun, especially if you are working with kids. Set up a special weekend day, grab some mini plastic swimming pools (or other portable lightweight tubs), dog shampoo, brushes, towels (for the dogs and the kids!) and lots of kid volunteers. Ask for donations to get your dog washed. This simple fundraising idea works great for kids, individuals, schools and animal organizations. You may also want to talk with local vets and pets stores to see if they can help out or participate in some way. Have doggy treats on hand and for extra revenue, you can even sell some dog related items such as leashes, dog bowls, etc. You can even hold a raffle for $1 or $2 a ticket and giveaway some pet related items, such as a doggy gift basket full of dog toys and treats.
Make sure that you require that all dogs be on leashes at all times, and that you clearly state this in your communications. You may also want to make sure you are covered by insurance in case anyone gets bit. Also, have some different type of shampoos available including hypoallergenic brands.