When most of this is done, you need to do the underside before finishing so get a second box style bike stand, make sure the fuel is off and lay your dirt bike down with the bars turned to full lock and grip resting on the box. You’ll see no end of additional mud on the bottom of the swingarm, bashplate, linkage – if you have one – and up underneath the mudguards, but don’t go mad on the linkage – maybe use a soft sponge to clean it to protect the bearings. Flip the bike to the other side and repeat.