Fortunately a local farmer is happy to have it. We muck out into a trailer & when full the YO takes the trailer to a nearby field & dumps it. It is then ploughed into the ground later in the year.
I have a friend with an allotment who takes a lot of mine (comes and fills his trailer) but I also put an advert on the intranet at work and I now have a waiting list . . . . I'm currently waiting for the current heap to rot down a bit. They bring me big plastic compost bags, I fill them and take them to work for collection.
We have a muck heap that lasts 2-3 years before needing emptying. We were lucky the local farmer took it all this year to spread on his land. Last time though he buried it for us on our own land which I thought was a good idea (his suggestion!) Only thing is you'd need to have a dip in the land to do it so you can put the soil back on top without having a huge mound and in my case there was a lot of stones to collect afterwards as it brought them all up!
Some blokes in a lorry come and get it and then they turn it into bricks (normal red bricks) and give us some back in exchange for the poo. I kid you not.