To avoid contamination, use the Spout Cap. If dirty water comes in contact with the Inner Press, wash the Grayl (not the cartridge) with soapy water and rinse thoroughly. Alternatively, dilute contaminants by pressing and agitating water through your GeoPress® Ti Bottle 5-7 times.
There are a variety of available methods to avoid cross-contamination during transfer of clean water into your Outer Ti Cup when preparing hot meals. Really depends on the environment you're in at the time you're preparing to prepare hot water. Below are the two most common methods.
Method #1. Purify and filter your water, separate your Inner Purifier Press from Outer Ti Cup; then wash your Outer Ti Cup with biodegradable soap. Disperse suds and lightly rinse with a little clean water before filling with clean water and bringing to a boil.
Method #2. Purify and filter your water, then separate Inner Purifier Press from Outer Ti Cup. Then dump excess water from Outer Ti Cup and towel dry the inside of the Outer Ti Cup prior to filling with clean water and bringing to a rolling boil.