Made by Air Head, this compact version of the urine bottle holds around 1 US gallon (just under 4 litres), although, it should be emptied before it reaches its full capacity. The bottle cap is optional as you may already have one from when you purchased your Air Head toilet. The smaller tank will save around 1.5 inches (38mm) in front to back space.
If you have the larger (standard) 2 Gallon liquid bottle already installed then the brackets would need to be moved to accommodate and securely located/lock the smaller bottle.
Please note that it’s not possible to exchange the standard 2 US Gallon container for the smaller 1 US Gallon container at the time of purchase – sorry!