I hate throwing things away, but I've now got lots and lots of 1 litre,

One of the chains of garden centres (Wyevale I think) were starting a
recycling service for pots. I don't think they were offering anything in
exchange although if you had loads you might be able to convince them to
give you a plant in exchange.

1. You could try to always grow a new plant from a cutting to give away to a
friend every time you buy a plant. That way you can give away the pot at the
same time.

2. You could cut them up and use as drainage material in the bottom of pots
just like you would with broken terracotta pots.

3. Plant them in the ground next to thirsty shrubs/trees. Water by filling
the pot. This gets the water down near the roots instead on top where it
evaporates. Then you're saving water as well as recycling the pots.

Martin