the silencers generally have a packing material (fiberglass, or something like that) to help reduce the noise level. Soaking the silencer probably won't be the best idea, as you will simple water log the packing material. If you have after market silencers where the end caps are riveted onto the tubes, drill out the rivets, pull it all apart, take out the packing material, throw it away (dispose of it properly as it's now a hazardous material with all the oil, or if your in Thailand, simple throw it in the trash ).

Then go down to your local dirtbike shop, and buy new packing material. Wrap up the core with the new packing, using safety wire to hold it all on the core tight and slide it back into the tube. Re-rivet the end cap back onto the tube and away you go.
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Charles Gallant