Recycling plastic bottles needs a lot of space

Kerbside recycling is pretty good where we live, but plastic isn't included yet, so we have to take plastic bottles to a collection point at the supermarket. It's mainly milk bottles, which get rinsed out in the kitchen, then get propped upside down in the garage sink to drain, before being crushed and stored in a big cardboard box until I take them to the recycle point.

Except that someone in the family (mentioning no names) tends to bung them in the box without crushing them, and I end up doing a mammoth crushing session in one go to make more space in the box. It gives me some exercise...

But the bottles don't stay crushed! They creep back into shape and fill the box even quicker.

It's like a pile of cuttings in the garden - there's not that much wood, but the sticks and twigs are all tangled and keep each other apart, leaving lots of space in between. Put them through the shredder and it turns into a much smaller pile of chippings.

If we could shred the plastic bottles, the chippings would take a lot less space, but would the recycling centre accept a pile of chippings? I think they're pretty fussy about not mixing different types of plastic, and a big pile of anonymous chippings is going to say "contamination", and "reject".

Plan B: what we need is something that squashes the bottles and then keeps them squashed. I partially achieve that by jamming the squashed bottles into the box, but that only works once there are enough to fill the box, and I want something that works right from bottle one.

I'm thinking of some sort of mangle-like contraption to squash the bottle, drawing it onto the top of a stack, which is stored in a rectangular tube with one wall that slides just far enough to allow another bottle in, but not enough to let the squashed bottles expand again.

The sliding wall could be held against the squashed bottles by a spring (would have to be a large one!) or a weight, or perhaps could slide on a mechanism connected to the mangle-handle.

The mangle rollers would need a bit more grip than those on a clothes mangle, as the plastic is a bit slippery. Maybe some little spikes (it wouldn't matter if the bottles were pierced).

Now, if the elves could just make me one overnight...