Second the comment about putting the blowoff tube on the gas post unless you want to spray beer all over. What works for me after fermenting several batches in cornies is to use a hop spider during the boil to cut way down on hop debris (relief valves and gas posts can and do easily clog), and shoot for 4.5 gallons into the fermenter with a 1.5 liter starter. Remove the gas tube and poppet from the gas side, shove a tube right over the post and into a blowoff growler. I leave it in there for a week or until active fermentation stops, then I put the poppet/gas tube back in, and throw on a disconnect with the tube in another blowoff jar for minor venting. I had a lot of growing pains and a lot of big messses during the first few, since following this procedure things have gone pretty smoothly.