As Dorota rightly remarked, some liquid in the waste vials is important, and not only for urea solutions.
The other thing which I encounter often when asked to come troubleshooting, is insufficient cleaning of the instrument. Whether you run Beckman, Agilent or another piece of equipment, please clean regularly
It will safe you a lot of issues. With simple, highly soluble and non-viscous buffers, once a week is often sufficient. If the buffer contains gel, urea, high concentrations of e.g. cyclodextrins, or is viscous for other reasons: clean after every sequence.
Often rinsing with water suffices. If you have an Agilent instrument, don't forget the prepunchers.
Furthermore, don't overfill the vials (max 3/4 fill height, see also the vendors manual) and please don't reuse the vials and caps with solutions that are viscous, contain urea or anything in high concentration.
All together, this should reduce the urea creeping around.