Hose Plastic foam surrounding the hose can be used to reduce heat transfer between the environment and liquid in the hose: keeping a cold liquid cool longer in summer and slows a liquid freezing in winter. Bite valve At least one manufacturer offers a tethered, slip-off, foam cowl that slows freezing of the liquid in the bite valve, and also reduces contamination of the bite valve. Filters At least one manufacturer, MSR, offers a in-line ceramic based filter, allowing use of local water supplies for refill. Ceramic filters can be cleaned at home by back flushing with clean water so no replacements are needed. Between fillings Scrubbing systems Sets of cylindrical brushes (e.g., a large one for the inside of the bladder, and a thin one with a flexible handle long enough to run at least halfway through the hose) permit mechanical removal of biofilm that will grow on the surface inside the system. Drying systems Means of holding the bladder walls apart to encourage drying between uses are available, such as a plastic frame that collapses to pass through the fill opening, but expands inside the bladder to hold the sides apart even near the corners. Techniques Various specialized practices may be applied in using a hydration system. Depending on the size of the opening for filling the bladder, it may be convenient to include, in hot weather, ice cubes or crushed ice when filling it. In theory too much ice means running out of liquid water while the bladder still has ice occupying space that could have been filled by more water (so it helps to take account of how temperature and humidity affect the balance between consumption rate and melting rate), but it helps that most people's tendency seems to be to put in less ice than would last through the hike. The use of liquids that provide calories (usually in combination with flavoring and perhaps rehydration salts) increases the cleaning burden by nourishing bacteria, and if the user neglects to empty and rinse the bladder, judging the cleanliness of the bladder at a later date involves more effort than with containers that are more transparent and in some cases more accessible. Some users carry plain water, with or without ice, in a bladder, but drink something else from Nalgene-style bottles during rests. On trips over a day, or in especially hot conditions, need for more water