Our MiniMed reservoirs come in 2 sizes for you to choose from based on your insulin needs. They are uniquely designed with a specific MiniMed connection, for a more secure insulin delivery. It is recommended to change your reservoir every 2 to 3 days. If your Total Daily Dose of Insulin (Basal insulin plus typical meal time Bolus insulin) is less than 48 units you may want to consider using the 1.8ml MiniMed Reservoir (MMT-326A) instead of 3ml MiniMed Reservoir (MMT-332A). The 1.8ml Reservoir is suitable for all sizes and types of MiniMed Insulin pumps including the new MiniMed 640G.