USB and 9V DC out of a sealed box
Using a cable gland is quite a normal way of achieving high sealing. You can combine the cables if you think this will work or use two cable glands: -



Here's one from Farnell (UK) that indicates its Ingress Protection (IP Rating): -



IP 68 means "Dust tight" and suitable for immersion in water beyond 1 metre

There is also an IP 69 standard: -


  German standard DIN 40050-9 extends the IEC 60529 rating system
  described above with an IP69K rating for high-pressure,
  high-temperature wash-down applications.[7] Such enclosures must not
  only be dust tight (IP6X), but also able to withstand high-pressure
  and steam cleaning. The test specifies a spray nozzle that is fed with
  80°C water at 8–10 MPa (80–100 bar) and a flow rate of 14–16 L/min.
  The nozzle is held 10–15 cm from the tested device at angles of 0°,
  30°, 60° and 90° for 30s each. The test device sits on a turntable
  that rotates once every 12s (5rpm). The IP69K test specification was
  initially developed for road vehicles, especially those that need
  regular intensive cleaning (dump trucks, cement mixers, etc.), but
  also finds use in other areas (e.g., food industry, car wash centres).


I believe you can get a few suppliers to supply IP69 gland. Here is a link to one.