It's kinda awkward to pour in fluid under the frunk, so hopefully this will make it easier.

 It fits really well, snug but loose enough for guaranteed fit by any printer.

I drew a compact washer fluid funnel for Tesla Model 3 using dimensions from thingiverse user hybrid999, but the shape is entirely new from scratch, steep sides, with channels for air to be pushed out the outside as fluid goes into the reservoir.

I printed PETG for a bit of bounce, and the model is very durable, 2mm thick overall.

For that reason, if you are good at PETG, you may even prefer to create an eco-version by using vase mode 0.8 path/over-extrusion with maybe >110% flow, and that could do the job.