If you are using a bottle to capture the urine then how long it takes to fill depends on how many people are using the toilet, how much they drink, how hot the outside temperature is and whether other toilets are used. Clearly a lot of factors! In general, allow 1L-2L per person per day and don’t leave it longer than four days before emptying as it may start to smell. It’s also worth noting that It’s recommended to rinse the bottle out every couple of weeks, just use a little bio-detergent and hot water and leave to soak in the bottle for a couple of hours, rinse again with hot water and put back in the toilet.