We use a plastic funnel, and a plastic water container. Put the funnel in the hole, and pour in the water. Without the funnel it's a 'dog's job' - and another very poorly designed piece of equipment. OH is an engineer, and these sort of design issues make him fume!
Another, also to do with the toilet, is the silly short drain tube and plastic bung which you have to remove to drain the tank. It's set so far back inside the cassette compartment that before you have any chance to stick anything around the drain tube it's sprayed water everywhere. A couple of inches longer tube would make all the difference. We now have a piece of flexible plastic which we use to divert the water, but it's still another 'dog's job' and either the caravan, or us, gets covered in pink toilet water!
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We (well - I!!) use a watering can. The tank will just take a full can. Our gas-bottle box is huge, so there's plenty of room to carry a plastic watering-can, and it weighs next-to-nothing (it's useful for re-filling the fire-bucket when the dogs have been drinking it too - saves having to carry the full bucket across the field 2 or 3 times each weekend!)
We use a pump/tube type thing that came with the van. It has an electric connection that plugs in in the waste tank locker and a plastic tube that goes into the freshwater tank (bit like your aqua roll pump).
Don't know its proper name though and cant seem to find one online. Will keep looking!
I was thinking the same thing, what would be the best way to fill that tank. I concluded the best thing would be an old water carrier we used to use for camping. Easy to fill and carry.
I unscrew the shower head then lean the pipe out the window, Kills 2 birds with 1 stone, It gets all the water primed through to fill up the hot water tank and I fill up the top toilet tank at the same time.
The shower head unscrews easy enough, just don't lose the washers out of it, take them out first.
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