Use a plug nug, (a little nug which blocks the hole) then pack your bowl. After you're finished, i would suggest emptying out all the water and then fill it up again. Making sure the bubbler's not blocked. If it get's blocked, use a cotton bud, rip off the cotton and jam the stick down the hole and remove the blockage. Also, hot water under the stem for a few minutes can get rid of a lot of rezin. A bubbler is fantastic, if it's clean and ready to use.