Disclaimer: I have not even seen the Trident, so this is pure conjecture
The concern with using the same vial would be residue from one test interfering with the next. This is strictly dependent on the test chemistry. If the Trident does use a single vial to run the tests I would assume that Neptune has addressed this issue.
Regarding cleaning, the frequent test interval may prevent buildup, the supplies may include a cleaning solution to rinse the vial afterwards, and/or there may be a recommended cleaning interval for the vail as part of routine maintenance for the system. Terrance would be the best person to answer this.