Yes, I was going to say the same as above - elevate the barrel.
A soaker hose works (use a filter on the water coming out of the barrel), but if you need to water lots of area, look into "T-Tape" by John Deere.
Myself, I'm piecing together an automatic 5-zone rainwater/city water drip irrigation setup. Rainwater will be pressurized with a 600GPH/40psi pump. When the reservior's empty (530gal) it automatically switches to city water. Looking forward to being able to leave my garden unattended for more than a few days this summer.