Waters SYNAPT G2 Operator's, Overview And Maintenance Manual page 51

Source interface door
Warning:
to connect the diverter valve to the ESI probe; use the PEEK
tubing supplied with the instrument.
7. Using PEEK tubing greater than or equal to 0.004-inch ID, connect
port 2 (the top port) of the diverter valve to the ESI probe.
Recommendation:
for sample flow rates ≤1.2 mL/min; use 0.005-inch ID tubing for sample
flow rates >1.2 mL/min.
When replacing tubing supplied with the instrument,
Requirement:
minimize the length connecting the diverter valve to the ESI probe.
Doing so minimizes delays and dispersion.
To avoid electric shock, do not use stainless steel tubing
To reduce peak broadening, use 0.004-inch ID tubing
Source interface door.
Configuring for ESI mode 3-5