Hippo bag and rain?

[felineweird]

Hi all

Random very boring topic but we have just got a hippo bag but my husband is worried about what happens if it rains, will it just get full of rainwater?

TIA if anyone knows

You mean one of those big, square, 1 tonne waste bags?

Yes it will fill up with rain, they are impermeable. Could you fold down a side so it can't accumulate rain?