Bathing should do it, but you need to discover the cause first. If it is a very long coated dog, maybe it needs clipping. If it is sh*tty round its bum, then it needs cleaning/clipping. But most important, if there is a bite wound or abcess that has burst under the fur, then this needs treating, as flies will land on it and lay their eggs, which of course turn into maggots.
I once took in a rescued rough collie, and when I went to brush it, it had an old bite wound on its rump that had become infected and was infested with maggots. Even the vet heaved as he cleaned them out - he flushed them out of the wound with a salt water solution.